What fluid for a 4-speed trans?

The close-ratio in my Valiant uses Penngrade GL-4 (formerly Brad Penn), partially because the spec sheets/web page specifically mention vintage musclecar 4-speeds. It's also about 1/3 the cost of RedLine MT90, which was my other choice. That car won't see cold-weather use, so no worries about the "paint stick in wet cement" sensation I had with 80W-90 in winter use.
I have a couple of bottles of Royal Purple's Synchromax fluid, which they recommend for any manual trans that calls for ATF. I shied away after I saw the GL-5 rating on it, though, only to find out later that RP doesn't use sulfur to achieve the GL-5 spec. Synchromax is safe for brass synchro rings. Since I already have it, I'll use that in the A833OD I built for my 170-cube '68 Valiant. The lighter oil not only shifts more smoothly, it's better for fuel economy.