Technical Big block Chevy ID

I have an old suburban that someone stuck a big block in but I cannot seem to identify it. The last 3 numerals stamped on the pad are 7FD. I cannot see the casting numbers on the back of the block as it is too tight to the fire wall. I tried using an inspection camera with no luck. It is chevy orange but could have been painted years ago. I guess I can cut a hole in the firewall if need be. It runs like a top. Also there are no serial numbers stamped on the pad so I suspect it is a replacement or a marine block.

 

Remove a valve cover to see the head casting numbers; that may also give you an idea what the engine might be.
I am Butch/56sedandelivery.

 

no idea what it could be with that limited info.

if it has a small damper, it's probably a 396 or 402. If it has a big one (with the weight on the back side) it's probably a 454.

If it has a weighted flywheel, it's also probably a 454.

 

It could also have an 8 inch damper with no weight and be a 427/425

 

yup, that's why I said "probably".

feel for the weight on the back of it...

 

Can you reach the rear pad to press a lump of putty on it? Then peel it off and read the reverse impression.

 

Can't reach or see the casting numbers. Small damper so its probably a 2 bolt 396 or 427. I guess I'll have
to tear into it to find out for sure. Got it for free so the price was right. Also has a 780 dual feed Holley
mounted on a square port weiand intake; I'll have to pull a valve cover to ID the heads but I bet they are
oval port. Thanks guys for the suggestions.