There are two kinds of voltage regulator- - - -"Delco-Remy" and "WRONG!" I'd rather have a good condition, properly adjusted 70 year old Delco than a wheelbarrow full of offshore made junk ones. Their failure rate, right out of the box, is somewhere around 50%.
www.ebay.com/itm/157140205091?Try connecting a jumper wire from the regulator "F" terminal to ground, and raise the RPM slightly. That should put the generator into full output and raise the voltage at the "ARM" terminal to 7+ volts. If the cutout relay is working properly, the voltage at the battery posts should also rise noticeably. Don't rev the engine much above a fast idle, as that will overload the generator.
Jerry