86 chevy 4x4 400 engine

[knifeman1]

im looking at an 86 chevy 4x4 truck that claims to have a 400 small block in it .
it has small 400 badges on the front fenders which i know doesnt mean anything . my question is : how do i look at the engine and tell a 400 from a 350 ?

[gGMC DOG]

look at the CASTING NUMBERS

http://www.73-87.com/chevy_ids/blockid.htm

[BigBlocksRule]

There were only 3 SBC400 casting numbers. They'll end in -817, -509 or -511.
If you can't see the casting numbers, look at the side of the block. A 350 will be relatively flat, where a 400 will have small "bulges" around each cylinder. They're not large, but the side of the block is definitely not flat.

[ont_guy_38]

If it is a 400 the balancer will have a cutout in it like the picture

[BigBlocksRule]

^ correct, unless somebody bought an aftermarket with the extra weight on the inside...rare, but it's happened. If you see the offset/cutout, it's either a 400 or a 383.
Good luck, hope it's a 400, they can be beasts!