I think you should stick with what the basic problem is and diagnose from there, if the starter does not engage and crank the engine over, find out why, the generator and the regulator supply dc volts and amps to the battery, I saw nothing about testing the starter? Hope this helps?
There is a reason for the saying ,Check it 7 ways to Sunday, and it has been my experience, that when you have that done, check it many more times and assume nothing and you will not be disappointed in the end.
This is something that I remember from my dad talking about 29's and similar designs,that when the fuel tank level is low that they would starve for fuel because of where the fuel tank feed line was at, the quick answer was to go up the hill backwards and it would not run out of fuel supply...