What exactly is it doing?
Heat soak and Vapor lock can evidence themselves in seveeral ways, each from a different heat source.
If the problem is a motor running too hot, and fuel boiling in the fuel pump, then an electric fuel pump to help move fuel through the rail and pump quicker helps considerable if you enlarge the return orifice to take advantage of it.
Wrapping the fuel rails helps even if you don't wnat to hear that, as well as wrapping the fuel lines to the CARBS and FROM the hard lines on the chassis rails. Isolating the metal hold-down brackets from the head with phenolic also helps with thermal transfer from the head to the fuel rail.
A cooler thermostat should help some, but if you don't have a heat-shield over the exhaust manifold, radiant heat is going to boil the fuel in the float bowls in heavy usage or stop-n-go.
Winter/Summer gas is a VERY good observation, especially at this time, our temperature out here yesterday was in the low 80's, yet we MUST be using the winter gas from oct to may, soooo.
Timing can have an affect on how hot the car runs, too much advance, and you heat the head, run retarded enough, and you have a glowing red exhaust manifold. So goes it with AIR injection, if it's pumping when it's not supposed to, you can really heat up the exhaust.
Headers? Well, you put 'em on--now you pay the price (o get maybe 2HP over 6500rpm...)
And last but not least, you can install a major-sized cool can made out of a 1 gasllon Igloo beverage cooler and some copper tubing. It will hold 7# of ice, and last about 1 hour driving at very high speeds, in very high desert temperatures before the ice turns to 120 degree water!
And this is with SU's right? If it's triples, the same things hold true, but there are a few more things you can do, depending on the brand...
Checked the archives yet?