You really should not put any belt on with the starter. You are stressing and possibly even cutting the new belt plus the fact that it is not properly adjusted. Your '81 has an R4 compressor and I agree it is a pain to adjust the A/C belt.
The power steering is loosened/tightened by loosening the bolts that run through the bracket and pump in a fore and aft direction. Once loosened, simply use the long stud and nut adjuster mechanism that extends out of the pump/bracket toward the drivers fender. After tension is correct, retighten the fore/aft bolts.
The A/C is more difficult and it would be much easier if the car is raised a bit. Ramps would work good for this. There are several large bolts that run fore and aft through compressor and it's bracket, and an adjuster that extends toward the drivers side front wheel is available on the compressor as well.
Be patient, take your time and you can replace all three of these belts, tension them correctly and be free of belt problems for many, many miles.
Best of luck,