You can make a ford 400 do want you want . first a few things, build for torque outright, good rod bolts and balance job, 2v heads must flow 250 cfm ,bowl blend intake and exhaust and short turn work in heads, find 2v closed chamber, open chamber and nitrous will cause problems.
I ran 6.60's in 1/8 mile with 351 c with 10.2 compression .555-.565 lift solid cam 235-245 @ .050 110 sep 106 c/l chet herbert solid, eagle rods , trw flat tops. ger 10 inch converter, flashed 4500 on 100 shot or 250 shot. 4,11 gears and 26 x 8.5 et street at 3140 lbs 68 mustang with leafspring suspension , southside lift bars 4v heads 2.19 1.71 valves bowl blended only, the 2v closed chamber would have worked better.
the car ran 12.20"s in the 1/4 on motor an 10.50 "s on dope 11.0"s on 100 shot.
the chet herbert cam was 75.00 and worked great, it pulled to 6500-6800 in my 351 ,in a 400 it will pull to 6000 easy.I would use a 10 inch 3000 stall, 3.91 gears and a 28 x 10 x 15 slick on your mustang.
start out small on the nitrous 75-100 shot 6.0 lbs fuel pressure and drop 2 degrees for every 50 hp jump. The stock rods will need arp bolts and I would not use more than 125-150 shot on them, use arp main studs, and a main gridle from ford performance solutions. I would buy a aftermarket bell housing and use a c-4 behind the motor , transking c-4 super comp version .
I could run 93 pump gas onn my motor and spray 150 shot to run 6.80"s easy shifting at 6100 with this combo.
mike stephenson
mstephenson@bluebon.net
979-251-8992