Steven,

I am certainly no expert on this subject so keep that in mind. There is no reason why you can't use the 925 generator and wire it as it would have been on a Master Series car. I'm not confident that this will solve your problem. The adjustable 3rd brush is the (alleged) solution. If it is set to keep up with your radio and heater, you might be over-charging when they are not in use.

I have a 1936 1-1/2 ton truck. I bought it to pull a 20 foot long Fruehauf semi trailer. I wanted to make sure my generator would keep up with extra lighting so my "electrical guy" told me how to add a regulator. I hid it so that everything looks normal under the hood. I can't report on the success of this conversion because I found and installed an original Chevrolet platform bed and never wired and pulled the trailer after that. I mention this to let you know that a regulator can be used in conjunction with a 3rd brush generator.

Mike

@35mike 

Mike. Thanks for your input. I think I will install the generator and light switch and  see what happens. My thinking is that Master models were equipped with the 925V  to accommodate the additional electrical demand, as options were installed as standard equipment. 
A regulator may end up being my best bet. 

Steven,

I can't think of any electrical demands that would be standard equipment on a Master that would differ from a Standard. Heaters, Radios, RH Tail Lamps, special horns, etc. were all accessories for either series. I hope the upgrade solves your problem.

Mike

Mike,  thanks for your last note.  If the electrical demands were not different, why do you think they offered two different generators, one with a special switch so that when the lights were turned on the generator accommodated the  demand?