Heo,
I put a TKO 600 behind my stock 390 in my 57 Ford Fairlane 500. I've put over 30K miles on it since 4/1/2009. If you pay extra for the short FE input shaft you have no problems making the swap. I use a 3.50 tru-trac and street tires also. I turn 15.2 @ 91mph (shifting at 4K) through the quarter and get 20 mpg with it on the way home from the race track or car show. It's the most amazing transmission you'll ever buy. I cruise at 60-65 mph @ 1850 rpm with that 3.50 rear end. I've got to be honest though, you'll spend about $4500 by the time you get you're drive shaft recut, clutch, pressure plate, new crossmember, special pilot bearing, throw out bearing, safety bell housing, flywheel, etc. But, it's the smoothest transmission I've ever sat behind at any speed. Jim