Fuel system issues

Having read the whole thread, I have to agree with Mad... It sounds more ignition related. Changes in the fuel system, if you're having ignition issues, will affect the ignition issues. You said it was spun up on a machine. IIRC, the slant is a gear driven distributor, off the cam. How's the distributor gear on yours? How much free play between the gear and the cam? Have you checked to see how much slop there's in the timing chain and dist drive system? Sounds to me like it's wandering at higher rpm.