I'll have to wait and see if my uncle gets the boss to the strip. He doesn't have the 9:1 CR, that's his buddy who had his motor dyno'd at the shop my Uncle had his engine built as well. The 9:1 motor had low compression piston's and the 1970 heads. In 1970 model's the Boss came with puny 2.19" intake valve's
. The reason the other guy's motor was detuned was so that he could run it on 87oct pump gas.
My uncle's Boss has ported 1969 heads, and a mild comp cam, since the engine was disassembled and had no cam in it. He did say it's really short on go under 4000rpm's. That, with the stock rev limiter would imply a narrow powerband.
400hp (gross) would probably mean 340hp (net) and roughly 290hp at the rear wheels on a Boss. Given the fact the more hp you make at the crank, the more you lose in the driveline from friction and drag, the net difference is always going to be smaller than the gross difference in hp. I'm not sure what the 1969 Boss weighed, but I believe the semi-hemi 302 was pretty heavy. The net difference in HP between the cars would be less than 50hp. According to your numbers on the 4.6L SOHC, which would seem a bit high?
Anyway, I hope you don't plan to argue 50hp on a heavier car, with a poorer start, and with a smaller powerband, should mean more than an equal trap speed.
If the Boss was launched well, and had the correct gears, 13's should be in reach.
Fortunately, the 428 big blocks aren't so fussy about powerband, they don't weigh much more, and they ARE geared for the 1/4. They routinely ran mid 13's bone stock in the Mustang.
The net numbers and rear wheel numbers are guestimates, based on less power loss from gross to net on a Boss due to lack of power steering, A/C, or large alternator. The rear wheel power is reflected in the fact the Boss never came with an auto.