Bob,
I agree with Al about blowing a 35 amp rectifier would take quite a lot. They will handle quite a surge without blowing. One option you might consider is using an isolation transformer between the outlet and the variac. That would put your power floating and make it safe to touch even (as long as you only touch one wire). I would guess the geco's would handle a couple of volts of ripple on the motor supply with no problem. A comon rule of thumb for capacitors is to always use one with a voltage rating that is about double the operating voltage. If you were rectifying line voltage of 120 VAC you must remember that is the RMS voltage. The peak voltage will be 1.414 times that or about 170 volts. With an unregulated supply the voltage will be higher with no load, and if you have never experienced a capacitor going BOOM, be prepared to check your self for aluminum schrapnel. If you ever hear this faint hissing sound comming from the direction of the cap's kill the power and leave quick (voice of experience
).
Steve