easy way to identify olds engines?

[midwestcutlass2008]

i've got an 85 with an olds 307 the roller motor. but i found a guy selling what he thinks is a big block olds, i looked at it about a year ago and he wouldnt sell it with out the rusted out car too. but now the car is gone and the motor is still sitting out back. i have no idea what a big block looks like to me all the olds engines look the same, it does seem to have a wider intake deck, but that might be looks because it doesnt hace the ufo size air cleaner cover on it.. and also where are the engine codes on olds motors? i know where my 307s head codes are. but not the engine.
by the way if it helps any the engine is light blue, well remnace of light blue.

 

[joe_padavano]

Look at the small shelf where the oil fill tube mounts. You'll find the block casting number. That will tell you what it is. The big block Olds motors (400, 425, and 455) use an intake that's about 14" wide. The small blocks (260, 307, 330, 350, 403) use an intake about 12.5" wide.

Big block casting numbers are as follows:

386525 A -- 1965 425
389298 B -- 1965 400 (short stroke)
389244 D -- 1966-67 425
390925 E -- 1966-67 400 (short stroke)
396021 F -- 1968-72 455
396021 Fa -- 1973-76 455
396026 G -- 1968-69 400 (long stroke)
231788 L -- Marine and industrial motor 455 (not installed in cars)