Sounds like other issues with the moder to me.....never had an engine with no issues that wouldn't run extremely well with:

1. Good Carb
2. Good Fuel
3. Good Ignition
4. Timing Marks Correct
5. Cam Degreed Correctly
6. Dizzy Phazed

Vacuum Leaks...????

Wipe Cam Lobe on Break-in...????

Have you done a leak down or at least ck'd cylinder pressure across all 8..???

Air
Fuel
Compression
Ignition

Try thinking simple and make small changes....????

sorry to hear these woes.....hope to hear better news soon smile

Rickster