I am posting this because It has been difficult for me to to find info on these engines. I began toying around with these engines over the last couple of years...I am building a 1962 cad 390 for my 36 ford. What I am sharing is my experience thus far, but I do not claim to be an expert! Feel free to correct me if I am misled; feel free to add to this post to help others!WANTED speed parts for 331-390 Cadillac engines!
The 331 was the first overhead valve Cadillac engine. Early 1949 engines had "center-bolt" valve covers rather than the perimeter style bolts common to later engines.
I believe that somewhere between late 54 and 1956, the 331 became extinct and the 365 was born. Although they are similar engines, there is a great deal of difference between the 331 and 365. The 331 has a portion of the bell housing cast to the back of the block like an Old's rocket 301...I believe they share the same flywheel (Olds 301/ 324 and Caddy 331) The CAD 331 only parts are:engine block, distributor, exhaust manifolds, and rocker shafts are different in appearance, seem to work on a later engine. I have heard the heads will interchange with later engines, but exhaust ports are smaller and spaced differently than later engines. 331 are lower compression than 365/390.
Interchangeable parts between 331 and 365/(390 through 1962) are: valve covers, valley cover, water pump, pulleys, valve covers intake manifold, timing cover and heads(but I believe push rods have to be altered and valve relief issues come into play)
365 and 390, up through 1962, are very similar. Only major difference is stroke/ displacement and the oil filter. 365 has remote oil filter like a 331 and 390 has a spin-on oil filter on the lower passenger side of engine block. Although NOT interchangeable with other GMs, 365 and 390 engines @ the back of the engine block where transmission mates are designed much like late model GM engines(ie small Chevy).
If you want to adapt a ford or GM manual/auto transmission to the rear of these engines check out wilcap.com They have just about any type of adapting combination one could conceive...just make sure you do not have a shy wallet!
1963 is a weird engine....
distributor is moved up front, much like a ford v8. Water pump was redesigned along with timing cover and valve covers are different than earlier model engines... I have 1963 heads on my 1962 390 and 1952 331 script valve covers on the 63 heads.
I believe the 429 was born from the 1963 390 engine???
Anyone know if 429 heads are interchangeable with 390????