Lots of reading for you.
How my car was wired. The relay is under the battery tray. Your 71 GT is probably the same.
Note the alignment.
It's not just an "Urban Legend", at least in the 70 FSM. It specifically says not to run the motor out of the car. They did specifically mention the limit switches.
I bet if you did like Bob said & just touched momentarily you could get away with it. I just test em' on the car since I have 2 with hiddens. To help simulate a load you could put a square-shanked screwdriver in the drive slot &give it some resistance to be safer.
Remember to turn the manual knob back to the alignment marks after testing, this puts the motor in the middle of it's range & you lift the doors to the halfway open position to install it. At least for a 70 anyway, I'd think the other years would be similar.
To clarify that a bit.....look at where the square shaft goes thru the gear housing to each door, There a little pip mark on the outer section that doesn't move & a pip on the center that turns. You just turn the manual knob at the bottom & line the 2 marks up with each other.
Bolt it up, slide the square drive thru, lift the doors ( you can do 1 at a time ) until the square drive falls into the slot in the doors ( doors should be about the half way open point ) Don't forget the spring steel retainers that slide over the square drive & hold them to the doors. Once both are hooked up, connect the wires , get in & turn the key on...doors should close if everything is working.
Headlights will come on without the key on but the doors won't open until the key is on.