I have ran the Summit 2802 in a 400 with 10:1 compression. I was running 3:23 gears at the time, and it had plenty of power all the way to 5700rpm or so. I also ran a stock converter. It had plenty of low end torque to smoke the tires. I'm sure it would have ran a lot better with a 2500 stall and 3:73's. I am not sure on the vacume, but it had plenty to run the power brakes. I would say that if you switched to 3:73 gears you could get away with either the crower 60916 or the 2802 with the stock converter. If you ran a ram air 4 or the xe274 you would need a 2500-3000rpm stall for sure. I would invest in a new set of valve springs. Also, unless you are running a domed piston, the 6x-8 heads on a 400 will yeild around a 7.6:1 compression ratio, a 6x-4 head will yield an 8:1 compression ratio. To run any of the cams that I suggested I would recommend atleast 9.5:1 compression, with 10:1 being the best.
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