I have a 64 Coupe.Currently running a 383 stroker motor with a Griffen cross flow aluminum radiator.(2 -11/4 tubes)Also aftermarket electric fan.Had Great results!Also recommend a high flow water pump.You may find that a restricter is a better bet than a thermostat.Also unless the after market fan has its own shroud,suggest putting on one for better draw thru radiator.Hope it helps!
As far as the 3:73 rear gears.Eckers does a nice job of rebuilding rear ends.But ,I currently run a 3:08,for less RPMs at freeway speeds.Drops your,"off the line",but it saves running over 3000RPMs at 65 to 70MPH.Hope it helps.......