I run a 104t 64p prs spur gear with a 40t pinion. If you use socket screws for the motor, you can get a ball end tip in there to adjust. Yes it is a pain.
The other thing you can do: take the top decks off, and take the layshaft off. Guess where you need the motor then put it there, tighten the screws so it won't move on its own, but will with a little help from you. Put the layshaft back in and adjust the gear mesh, then take it back out and tighten the motor screws completely, then reassemble.
Yes, it is a pain, but where there is a will there is a way.