Putting money into the valiant, suggestions?

I had good luck with a Painless harness, but I did TOTALLY replace all the wiring and used aftermarket gauges and ignition. Although you could do wiring, there are other places I would worry about first.

I would convert to electronic ignition. Nothing fancy needed, just decent used parts. And follow the typical wiring diagram to get it hooked up. Preferably wire it as a single ballast, four pin. Buy an extra ballast resistor and carry it in the glove compartment.

Brakes are at the top of my list. I would convert to front disk, then do a typical brake job, plus replace all the hard lines and hoses.

Modern seat belts are a good idea. I'm using some from www.wescoperformance.com

If it doesn't have one, put an anti-sway bar on it.

Flush out the cooling system. If it's at all marginal, replace the radiator. Bad radiators suck.

Obviously good tires and battery, but that should go without saying.