Top End Miss

Sounds like you're on your way, but I'll throw a couple of other ideas out there in case you're not sick of trying stuff! LOL

Have you done anything with the coil? I saw you changed box, cap, and rotor...

I would recommend checking the coil wiring also.

I would really closely check the grounds and such in the car, especially if the battery is relocated (and if it is, make sure you still run a ground wire from the block to the body in the front where the negative cable used to be).

I had a problem with a high rpm miss that I chased all over. It turned out to be the ground wire from the relocated battery was either not heavy enough gauge, or bad wire. Changing it for a bigger wire, extra clean frame hookup (after I tried everything else) all of a sudden the car would go as high as I wanted.

Of course it just might also just be the lobes are too aggressive for that kind of RPM with a flat-tappet lifter, no matter what the spring pressure is, but that would be a fall-on-its-face thing, rather than a miss or "breaking up".

Good luck, sounds like an awesome combo.