You are chasing your tail. Changing coolant is good for maintenance, but would not solve your overheating, and you need to determine the actual cause of the excessive heat or lack of cooling. Causes for overheating at low speeds are many and often multiple, but range anywhere from incorrect idle ignition timing, to missing shrouds, failed fan clutch, scaled passages, slipping pump, leaking gaskets, blocked radiator passages or fins, and more.
I would verify your timing marks are correct, set base timing, check timing at higher rpm for proper advance; then take it to a respected local radiator shop or classic car mechanic for diagnostics. They know what to look for and how to test in order to determine root causes without applying band-aid solutions. The Ford Shop Manual set for your year is priceless for diagnostics, and you can do it all yourself, but it's up to you if you have the determination or time for that. I am only suggesting you fix your issues so it does not boil-over in the first place, and then you can use whatever coolant makes you giggle.
BTW, Puttster is correct that distilled water with anti-rust/pump lubricant additive ($3, or something like Water Wetter) is a more effective coolant with better thermal characteristics than anti-freeze in warm weather. If using anti-freeze, use only the recommended ratio for your anticipated temperatures, for best cooling. The more you use the less efficiently it cools. While many like anti-freeze or waterless coolant to inhibit embarrassing boil-over and driveway puddles, I could not care less about that (I actually want
that) because I'll fix the boil-over cause, and want the best cooling and engine safety. Boil-over is part of the original engine protection scheme, and explanation of that is in other threads here. That's me. Do your thing!
From this chart, you can see that a 50/50 mix of anti-freeze has about 87% cooling capability of straight water, and 66% with straight ant-freeze: