for what its worth my machinist said for a good bracket motor he prefers the standard Wix because of better filtering only uses the R filters on all out race stuff.

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