470 runs out of steam at 5100 rpm

headers (with dumps) are not choking, FAST guys are running low 10's through manifolds. A donut says your fuel delivery is suspect. 2nd guess would be ignition. ignition is easier to swap out with another box. FBO says MP boxes do a number on advance, ie. pulling timing out at higher RPM's/ I guess you could crutch that by bumping your timing up a few degrees before a test run to see if it helps any.