For testing you'll need a similar rectifier from a 720 or smaller. I think there is a procedure for testing the rectifier and the stator with an ohm meter, it should be in the manual.
The service/shop manual section 8-3 states that there are voltage regulator components imbedded in the rectifier so measurements of the individual diodes in the rectifier would be almost impossible. The manual references using the "Bombardier Ignition Tester" which I do not know if it is available.
I highly recommend that you insure there are good connections from the rectifier to ground and to what the wiring diagram indicates is a 15a fuse in the electronic module.
Section 8-3 of the service/shop manual indicates that you should have .05 - .6 ohm across the yellow - yellow/black leads going to the magneto.