So very stuck...

You don’t seem to understand how ignition timing and advance (static and mechanical) work. As engine speed increases you need to light the fire sooner (BTDC) to give time for the burn and expansion of gasses to act on the piston at the right time. At idle there should be no mechanical advance. So if it reads 5* then the timing is at 5*. Now if you hooked the vacuum advance to manifold vacuum it will pull in timing at idle. But you should not be concerned with that level of tuning at this point. Unhook and plug the vacuum advance for now. It should not take “all day” to set the timing. Before you do anything else, verify that your TDC mark on the balancer is correct, and that your brother put the timing tape on the balancer correctly. What ignition system and distributor are you using?