Re: 390 occasional overheating
What was the RPM you were running when it got hot?
Water pump is a smart idea, but I would also look at ignition timing first, make sure you aren't dealing with a stuck advance, or someone who may have set initial with vacuum line connected, retarded timing builds a ton of heat under load. You said you checked timing, but I would run it as advanced as it can handle with the load. Stock is in the single digits, even running heavy they can likely take 10 degrees initial
Second, depending on the fan you are using, you can move a lot of air or not much. If you are going to work it hard, recommend as big of an aftermarket not flex fan as you can fit.
Finally, the water pump is a great step after.
70 Sportsroof, 427 FE/489 cid, TKO-600, 31 spline 4.10, A/C. modified Mass-flo EFI/reprogrammed A9L/CnC ported Victor.