I think I posted earlier that your two 8R2 ohm resistors were 50% and 25% off value. They were probably 10% tolerance parts to begin with, which would be fine. Even a tube amp with resistors 50% off value would have problems.
In answer to your original question, I pulled one of my Frankie heads and checked the rectifier diodes. This one has Westinghouse 368D diodes. According to my NTE book, they can be replaced with an NTE5896 diode, which is rated 200 volts at 16 amps.