I'm not a guru and I can't answer in a manner that is very detailed, but...

If he pulls the trans, removes the torque converter (slides out) , and unbolts the front pump, sets it on his bench, then carefully removes the forward gears, he will be right @ B3. It takes about 20 minutes to reach this. He probably only needs the frictions, and they are only like $2.50 each. There should be 4 I think. He then can bolt it back together and it will have reverse, unless some other problem other than wear caused the frictions to wear out. I fixed a 722.507 last month like this in a 1996 SL320 w/slipping reverse.