Percolation? Heat soak? Don't drive during summer??

You do not need a fuel return line. You need to look at your cooling system.

Have you ever checked your radiator ?
Is it clean and flowing properly ?
Do you have the correct water pump for an AC car with the correct AC water pump pulley ?
Do you know the water pump is functioning properly ?
Do you have the correct fan, fan spacing ?
Do you have a fan shroud ?
Timing set properly ? 12-34 for your mild engine.
Water passages in the block flowing properly ?
Thermostat ?..In Vegas, run a 160.
These are things you should be looking at for your car running hot. These cars from the factory, box stock, use to run through the hot deserts at full tilt boogie without a hiccup.