Examining a few diagrams, I doubt if you can get more than 1/4" increase in cam bushing OD (not enough wall thickness), which will only move the cam itself up by 1/8". It's got to help, but it's a huge amount of work for not much extra room. It might help to offset it laterally - like Chevy did to the 250.
You don't need to match the timing gear C-C distance if you use:
1. an idler gear (and a reverse cam)
2. chain drive (and a reverse cam)
3. a much smaller diameter timing set and 2 idler gears (with the original cam)
