I think from another thread you used raingear? Did you call them? One of the first notes in their instructions is to call before you modify things.
I built my own motor assembly very similar to raingear but with stock wiper mounts and linkage. Getting the relative lengths of the crank arm length on the motor and on the reciprocating bellcrank right is not trivial. There is very little difference between getting full wipe and over centering the arms so the system jams.
So I'd call them first.
If they are no help I'd look at this arm to investigate slotting the mounting hole to allow effective length of arm to be made shorter.
Watch it run first to see how close to 180 it moves, too close will jam
Slot it, adjust it until dialed in then spot weld the washer in place to lock the adjustment
Assume you will take that motor out several times to get it right, so plan to make it easy on yourself, take out speaker grill, instruments vent arm, seats, whatever gets in the way