are you running the regular felpros or the performance ones I am running the felpro performance part # 1008 on a 416 with 12.8-1 timimng locked at 37 degrees and have had 0 problems so far.

70 duster full chassis super pro 416 CNC Indybrock heads 727 w/brake

best so far 1.212 60 6.219 in 1/8 at 110.88 9.768 at 137.81 1/4