Glen, Don, Dave, and Pat McCarthy and Jerry Clayton can steer you down the straight path, it's what they do to make spendin' money - it sure ain't very narrow, though. I'd like to toss my two cents in, though: in my experience, as to cams and their manners, what might be getting pretty "edgy" in a 350 will turn out to be quite "mannerly" in a 400. I had 400s in most of my work trucks, and never left them be, I just had to mess with them a bit, and they are good engines in my estimation, and make great street/strip pieces. On a different note, the T400 you have will rebuild into a nice heavy duty trans with just the replacement of the output shaft and tailshaft housing from a non-four wheel drive, and a good performance upgrade build; not a tough thing at all.