I’ve got a 500” RB with 12.5 cr that I use a starter from a V6 Dakota to crank it with. I’ve done it both ways a distributor with only 5 degrees of timing that would go to full advance as soon as it was running and then I switched to a distributor with 27 degrees of advance giving me 20 at idle around 950rpm and 37 at 2500 rpm. I’m not sure what advantage there is in doing it this way because it’s all under the converter stall speed of 4000 rpm. The engine has always started easy sometimes on the first revolution, I use a group 24 battery in the trunk with a quality relocation kit.
You don’t say how loose your converter is, but you could try backing the timing off until the engine started easy, this should give you an idea what to do.