[1963c-10]

Only things I know about the caddy engine....brother in law had a 68 w/472.
75-76 from the factory were all 500's except for the Seville which had an EFI olds 350.
67-69 all cars came with 472
70-74 Eldos came with 500's others 472.
67-69 same block
70-76 same block (minor changes to oil system and clearance for 500 crank)
67-73 small chamber heads (high or low comp depending on pistons)
74-76 large chamber heads (low comp only)
472 & 500 different crank and pistons otherwise same

I helped him out with the car a lot and the caddy guys here said that the 368, 425, 472 & 500 were pretty much the same engines minus crank and rods.

I know the HEI was standard on these engines in 1974 and if its a factory HEI then its probably a 500. I know you said it came from a 1971....do you know which model? My guess would be its a 500. I don't know if it helps any, but its what I can add to try and help you. You should be able to find some caddy forums that may help more with the engine ID.