Another test trick with Lycoming belt driven charging systems is to
drive the alternator only with a 1/2 hp or more hand held electric
motor instead of using the engine. The direction of rotation isn't
critical. If you want to have "variable" speeds, put a cone pulley on
the motor.

This makes it a lot easier and safer to work around. Disadvantages are
getting access if your cowl doesn't split, but of course that is always
a problem.

Recognize though that in service the alternator spins probably close to
10,000 RPM.