When you go to the 6 speed I wouldn't go any bigger than a 650 DP an you're liable to have to jet it back a bit. The 289 I have in my Mustang has a Comp cams 268H grind and an old 650 DP. I believe I've got 62's in the primary and 66's in the secondary and it's still a tad rich. I think I'd opt for a 600 DP if you want to run a Holley. BTW, tech hates the cam as it's just a bit lumpy.