If it's a stock 2 row radiator, then I'd go
with a 3 row. Keep the shroud as it will help.
Also if you haven't flushed your cooling system,
you might do that also. I used a Prestone flushing
kit on mine, does a real good job of backflushing
the system. What degree thermstat do you have?
I wouldn't go below a 180* t-stat.
I've got a 66 with a 302 in it, my setup is
a 3 row, shroud, clutch fan, & 180* t-stat.
I rarely go above 195* in stop & go traffic.
And yes I have A/C too. Good luck.
The latest thinking on coolants is to lower the anti-freeze ratio, especially if you live in a mild climate. Most people now recommennd no more than 20-30% anti - freeze, distilled water, and 1-2 bottles of water wetter. Just flushed and refilled my system that way.
An overflow tank can be helpful but is not absolutely neccessary.