After I rebuild them, I start with 1 3/4 turns out, and it never fails that I will need to turn them out more than that for optimum performance. You won't hurt anything by starting with 1 1/2, but that is just a waste of time.
Anyway, let us know what you did to get that Mustang from smoking. If you are dying at stop lights, it could be more of a problem than adjusting the carburetor. I would rebuild the carburetor and set the timing, replace the spark plugs and wires, and if you have the points system still, either put in a new set of points and condenser or replace that old technology with a Pertronix system, then see how that puppy performs. Yes, this stuff costs money, but nobody ever promised optimum performance from these old engines without proper maintenance.