Finetuning questions - do I need a high-stall torque converter ?

Simple test, start car, get it warmed up. Twist distributor at idle a little CCW, if it picks up RPM it wants the timing.

I think you are still short on initial timing. 10* is stock 318 territory from the factory. You have a larger camshaft. Should be in the high teens low 20's. Use the black bushing. Give the car 16 initial with the black bushing and see if it starts OK when warmed up. It should run even better down low.

I still have some 14* bushings as well. MSD missed the mark on not making bushing to reduce mechanical timing.