First off, you are not doing a "restoration" if you are putting a Chevy engine in a GMC.
Second, it seems strange that the front mount was moved forward since a Chevy engine is shorter than a GMC engine. Even stranger, you say it looks like the engine was moved aft an inch. Doesn't this contradict the first statement?
Originally your pedals were mounted on a bracket that attaches to the bellhousing. Sounds like a later bell housing was used and brackets cobbed in.
The front cross member of a GMC is different from a Chevy to accommodate the longer engine.
Why not find a GMC engine with the correct bellhousing? This will simplify things considerably.
