if the generator is in operating condition and no damage to the fields, etc..and it can be bench tested to produce power, then that leaves the rest of the issues to the vreg, wireing and battery.
with your statement of 2nd gen and 3rd vreg... you ain't got something right... and I doubt it's the genny.
lucase gennies aren't my favorite.. but they work ok.
lucas regs are pretty junky in my opinion.
you CAN get a working veg...
function of a genny and vreg can be as simple as the rest of that old technology on that machine.
I've never 'had' to convert to a alt because I couldn't make a genny/vreg do what i wanted it to do.
i HAVE converted to an alt before for other reasons however ( starting from scratch , or unable to locate an affordable replacement..etc.. )