I just acquired what I think is an old 396.  I've been researching the casting #'s on the block and it appears to be either a 396 or a 427 from 1966.  I've found "Hi-Perf" stamps in a couple of places and both  "PASS" and "TRUCK" stamps.  Does anybody know how to get a better idea of whether or not this may be a 1966 4-bolt main 427 without tearing into it?  I guess what I'm asking is; how much information can be gleaned from just the casting numbers and stamps?   The block number is 3855961  

Go to www.mortec.com as these guys have everything about casting numbers you could ask for..

Good luck!.........  

Here is what Mortec listed the blocks as:
(3855961....396.......65-66...2 or 4 bolt)
I hope this helps..  

Sounds like your motor has a mix of parts.  

There should be an application code stamped into the block deck surface just ahead of the passanger side head. Usually a two or three letter code.
However,  if the block was ever decked, those stampings will be gone.  

its a 396 1966-1967 2 bolt main in varies for hp depending on what car or truck it was in. On the low end it has 222hp to 325hp all depending on the car or truck it was in. there should be a suffix code consisting of 3 or even 4 letters to help u identify it even futher! try chevymania.com I hope this helps u out the site is awsome it well tell u everything u need to know  

My MSA-1 book says something similar to joshthechamp101; it's a two-bolt 396 with the only difference being the years with a '65-67 over '66-67.

Thanks for the URL josh, I'm going to check it out in a few!  

you can tell by the bore a 427 shares the same bores as a 454 4.250 i cant remember the exact on the 396 but mine was just a tad over 4.0 inches maybe 4.090 something also you can use a 396 crank in a 454 making it a high winding 427