RE: Three Inch Drums
As easy and cheap as it was to put the late 70's spindles/disk brakes on my '59, I'd think that'd be a better swap than the drums. Given that it seems the ball joints seem to be the same on all these, you could probably, if you have them, simply swap out the spindles and all if you're set on using the 3" drums.
How does your modified 390 pull the 'Bird? I was a bit dissapointed with the 5.0 HO I put in mine. It's a bit lacking in the torque department. I guess I discounted the add'l weight of the 'Bird as opposed to the 87 Mustang GT the engine originally powered! I didn't think it'd be that much heavier, but, it's still probably almost half a ton more. Steeper gears would help me, as I have the AOD trans.
I'd originally planned on a supercharger for the 5.0, but other projects have sidelined hot rodding this engine.