Since you do not have a scope, the timing light with two boxes will work.
What "boxes"??? I don't have any "boxes" that I know of...
Sorry you do not want electronic advance. It will give the grunt off line to burn tires and snap axles. I HAD axle-snapping performance off the line with the 3.55 gear I had in the car. My problem is with the area from 10-feet from the starting line to about 50 feet from the starting line, with this 2.76:1 gear. I don't want wheelspin (that's one of the reasons I got rid of the 3.55) but, more torque than I have now. More stall speed will give it to me, I THINK. You need to have normal advance or more, without boost, that retards as needed,Timing varies smooth with boost, not a switch in affair. I don't think that will mattter. Retarded timing throws more heat at turbo, but also reduces burn in cylinder centered on power stroke. Proper controlled timing results in a super strong torque curve. It will pull like crazy, and want the load, of up shifts. If you want to keep considering mechanical considerations, try boost retard dash pot on distributor. That might require significant fabrication, considering the need for adjustment compensations. The only dash-pots I have ever seen operated the throttle butterflies. I don't know what you are talking about.
The EFI controls also play an important part, but that involves electronics too. Having timing and fuel controls on a 3D surface of MAP and RPM with temperature related air density and timing enhancements, is much different than two locked timings on a switch and a carb. You have done such a nice job building your car, then leaving much HP on the table due to primative controls.