Updated: Mar 14, 2021
theres a whole lot of different nailheads... heres some tips i use to help me quickly identify them, without using casting and stamping numbers. the early engine casting numbers can be very vague, especially. if you see a nailhead with round exhaust ports and 3 bolt engine mount bosses, its going to be a 322 or 264. 1953 is one year only, and has mostly 1 year specific parts. from the outside, you will notice a window on the bellhousing skirt behind the rear of the drivers side cylinder head, used to check the timing for that year only. very early 53 also had a cast iron crank pulley, somewhat similiar to the 264. 53 also has a pass side exhaust manifold that the generator bolts directly to. 53 water manifold's thermostat housing bolts are square, straight across and not diagonally like all the later nailheads. the 264 came out in 54 to replace the straight 8. all the cars are now 12 volt, including the special that was 6 volt still in 53. the 54 and 55 264s all had 2 barrel carbs from the factory... but the dead giveaway is the cast iron crank pulley and longer timing pointer to accomidate the iron crank pulley. the 322 balancer used a stubbier pointer. all 322s from 54 to 56 use the same balancer. physically from the outside, it can be hard to tell a 54 from a 55 engine from the outside. 54 and 55 engines both have the same water manifold with heater nipple pointing to drivers side, like the 53, but therm housing bolts are staggered now... and timing cover with two nipples on the same side for trans cooler (like 53.)., and early water pump pattern. all 53s, 54s and early 55s had no breathers in the valve covers and sported the shield sticker. late 55 and 56 had the breathers that pointed straight up and no breather in valley. if you see a 322 with the heater hose nipple pointing to the driver side on the water manifold, and breathers in the valve covers, its going to be a late 55. other late 55 upgrades (not all) is stronger rods, drilled out pushrod holes and some have 56 intake manifolds. there is only variations of the 322 in 56. all 56 engines have the heater hose nipple relocated to behind the thermostat housing, which is the easiest determining factor that stands out. and no trans cooler nipples on timing cover. later water pump pattern, and breathers in valve covers. 56 was the first year for 2 bolt exhaust manifold collectors and used the "ball and socket" style exhaust pipe connection that followed through to 58. 53 plug wire covers are 1 year only with no slot on top. wires came straight out the back unlike 54 to 56.
as for 364s, theres 3 different physical 364 blocks. all 57 to 66 engines have rectangle exhaust ports and 4 bolt boss engine mounts. ALL 364 water manifolds have an extra vertical boss on the water manifold that points straight up on the drivers side. (very early 59 401 does too, so take note of that.) 57 to 58 364 blocks are the same outside of early 57 having a 3 bolt balancer and smaller dipstick hole. early 57 had short production valve covers with the difference being the mounting holes didnt use a grommet. 57 364 also has a 1 year only water manifold that the top pass side bolt boss into the head is shorter than all following years. otherwise, the easiest identification is the 8th inch pipe plug fitting behind the oil filter housing used for the vacuum pump hook up. also theres recessed casting behind timing gear that mimics the 322 and still uses the oil slinger drip guide that buick found out didnt need to be there (if you're looking at a bare block.) for the sake of keeping it simple, 57 and 58 are the same engine. starting 59, the 401 was introduced. theres essentially 4 different 401 engines. if you ever get a 401 or 425 side by side next to a 364, the difference in deck height which can be measured visually between the cylinder head and valley pan is the obvious indication. the easiest way to tell a 59 from a 60 engine, is the 59 used the 57 and 58 cylinder head casting with the straight thread temp sender. they went to pipe thread in 60. all straight thread earlier heads, had the temp sender mounted in the rear on their respective applications. otherwise, for the sake of saying so, 59 to 60 401s are the same, and 59 to 60 364s are the same, im not going to get into exhaust manifold differences between years... but easiest identifying part is the slanted spin on oil filter housing (first years of it.) 59 to 61 all have the long snout waterpump which is also a dead givaway. the 61 is a one year animal, all its own, for both the 364 and 401... and its the last year of the 364.. its a rear sump like all previous nailheads, has the long waterpump, BUT uses the 61 to 63 starter on the 61 to 66 bolt pattern AND uses the later oil filter housing that points straight down. so if you think you've found a 59 or 60 for your car that youve been looking for, and you see the late oil filter housing, you know its a 61. for the sake of keeping it simple, we will say 62 and 63 are the same and still dynaflow crank engines. all 62 are 401s. 2200 (or so) 425s were released special order in 63. so if you've got a untouched 425 with a dynaflow crank, you know its a 63. blocks are all the same from 62 to 65 otherwise. the 425 is its own block. all 425s have a casting trapezoid lump above the upper bellhousing bolt on the drivers side ALL of them have that. (not to be confused with other casting lumps on 66 blocks that 401s often have. 64 to 65 engines are essentiually the same. same as 62 to 63 except now theres a 400 trans crank with smaller hole in flange and flexplate has a ring gear starting 64. all nailheads are center sump starting 62 except GS skylark in 65 and 66. skylark 401 pan has a dimple in the middle of the pan (which didnt need to be there) and huge engine mount adaptor brackets. 66 was the first year of the smog pump. 66 are very easy to identify. only year with a chain loop on water manifold and chain loop behind the block behind drivers side head. factory replacement blocks typically have the boss for the chain loop, but the hole isnt punched. 66 heads are 1 year only. CA cars had air injectors. all other heads had the bosses for the air injectors, even thoough they werent present.
hopefully that rant is helpful. bear in mind most parts are interchangable between engines. if you find a core thats been "hot rodded" back in the day, its not uncommon for there to be a lot of mixed up or mismatched parts, which can make identifying it and figuring out what you have a little harder. i could also write a 5 paragraph essay on all other differences but i think it would just make this perticular article that much more confusing, as im just trying to focus on visually identifying them from the outside, quickly.