How to Know What Size/Year Nailhead You Are Looking At
I get lots of questions on this, many website's have casting #'s listed but have missing numbers or incorrect info such as the 705 (last 3 #'s in the block casting numbers) 401 block listed as a 425 block, that is WRONG, all 425 blocks have a casting number ending in 704. My Engine Building gallery pix show the casting lump on the back of all 425 blocks, that signaled the factory boring bar to go to 4 5/16".
OK so you want to know what size the engine is quickly? measure across the intake manifold bolts from left to right on bolt centers, 9" is 401-425, 8 5/8" is 364 and 8 1/4" is 264-322. If you have a bare block use the bore size: 264 (3 5/8"), 322 (4"), 364 (4 1/8"), 401 (4 3/16) and 425 (4 5/16).. Beware you could have a bored out block! Max overbore is .060 on all blocks except the 425, we try and keep them at .040 oversize as a max. Most over sized pistons have a stamp on top with the size. FYI don't forget to check for a crack in the block behind the starter, common in colder parts of the world.
The 264 came with a cast iron crank pulley, most 322's came with a damper and bolt on pulley. Just to make it more confusing the early 53 322 also had a cast iron pulley but no timing mark, you timed the 53 through a hole in the bell housing, just that one year. The 53 322 had many one year only parts and the block was just one of them, poor head and piston design so avoid the 53 322 or upgrade with 54-56 heads and pistons. Another thing that separates the 264-322 from the 364-401-425 is the engine mount bolts, the 264-322 engine has 3 bolts on the block and all others have 4 bolts. The 1953-58 engines have cast iron timing covers (all later ones were aluminum) and cartridge oil filters. The 59-61 Engines have really long water pump snouts and spin on filters, the filter hangs on an angle in 1959-60 and straight down on 1961-66. All 1953-61 engines (and 65-66 GS Skylark) have a rear sump pan. All 62-66 have a center sump pan (except 65-66 GS). The 1962-66 have a short water pump. The 1964-66 Cranks have a smaller hole for the st300 and st400 converter.
This will allow you to get much closer to finding out the year than casting numbers will. The 1957-66 engines also have letters stamped in front of the valley pan on the top of the block. One letter tells the year and another will give you size and horse power. I am not going to list them all but D is 57, E is 58 all the way up to M for 1966 on the later 401-425 a second letter tells the HP and size so "T" is a 325 hp 401, "W" is a 340 hp 425, "X" is a 360 hp 425 (Super Wildcat) and "R" is the 65-66 GS 400 (401) and then in 1966 there were some special HP options like "U" and "S" but these are super rare and most likely you will never see them. So if you have a 1964 Riviera, it should have two letters stamped on the block a K (64) and a W (425) or a rare X..
All 53 V8's were 322 ci. All 54-56 model's EXCEPT the 54-55 Special came with a 322 ci. all the 54-55 Specials came with a 264 ci. All 57-58 models and 59-61 Le Sabre's came with a 364 ci. All other 59-61 full size models got the 401. In 62 the only Nailhead engine was a 401 and from 63-66 both 401 and 425's were used. Looking for a 425? all 64 and 66 Riviera's came from the factory with them, they were optional in 63 and 65 Riviera, 63-66 Electra, Wildcat models. Still need help? please call us...There are (7) different 322's (counting the 56-59 GM 322 truck engine) and (3) different 264's, (3) 364's (4) 401's and (2) 425's! And that is taking into account 2 barrel, 4 barrel and 2-4 engines, boat engines and the ones that came with a factory stick shift , those had lower compression, and a smaller hole in the rear of crank for a pilot bearing up until 1963 (no stick shifts in 61-62). The 64-66 crank had an adapter pressed into them for a pilot bearing so all 64-66 cranks are the same.