@Gary's 67 I've been running the same pair of Sylvania halogen H6024s in MyFirstCar since 1992. I only replaced the original headlight switch in 1999 because the dimmer dial came apart. They're brighter than stock (MyFirstCar had the original bulbs in it when I got it) and I see well, but I'm considering adding LED headlight bulbs in a vintage-looking housing for the classic look and the modern light color with A LOT less draw on the electrical system without having to use relays.You might get away with it for a while, but you'll need one eventually.
Ron Francis has kits. However, it's just knowing the schematic and adding Bosch Relays. I did this a number of years ago, if only, to take the "heat" off my OEM headlight switch.Your favorite Mustang parts vendor probably has a kit. Or, you can search threads here and make one for yourself. Easily done.