[tv_larsen]

Basically, the difference is deck height. The RB's have a taller block to accomadate a longer stroke. Because of this, the intake is wider, and the distributor and push rods are longer. They also have larger main bearings.

383's and 400's are examples of B blocks, and 440's are RB blocks. Does that help?

 

[tv_larsen]

There were a few RB 383's made. RB 383 engine 4.03" x 3.75" stroke.

Are you sure? I've never heard of such an animal. Actually, that sounds like the bore and stroke of a Chevy 350 stroked to 383 cubes.