You may find by taking the lid off the motor all you need is a new set of brushes and / or brush springs........
I'm kind of assumming the relay(s) click when you hit the switch, just no motor action. If not, maybe relay or switch gubbed? Again assuming you've checked all the connections......
Is it a 3 ram unit? They were remarkably widley used 50-90 Hp and all in between for a while.
If it's any help, I have a set of clamps & swivel / tiller assy off a 70 (PT unit already sold I'm afraid) should you find a PT that won't fit yours.