This is all great info. Both dh & I tend to be very cautious with all things electric.
Never looks good when a fireman has to put in a call on his own structure :-)[
The clutch motors that came on the 31-15 and -20 machines are pretty sturdy motors.
Since it has been sitting for years you can expect a lot of dust in the inner workings. This will
smell and maybe even smoke lightly when first run.
Personally the first thing I'd do is to very carefully check the wiring from the wall plug to the off-on switch and from the switch to the motor.
The motor is probably very dry so will need oil. A drop or two on each end of the main shaft to start. Look for an oil reservoir with wicks, it it has one this needs to be filled and the wicks primed by dripping oiling along their length.
Then I'd take a paint brush and dust off every part of the motor that I could reach.