Timing an engine with feeler gauges?

In theory, can I time my engine with a machinist square across the top of the cylinder and feeler gauges?
I have been trying, realizing that there is a .019 gap at TDC between the square and the piston, by stacking a .035, .030 and .019 to set the BTDC of .065 (from the Tec. book Tecumseh H30) and using a volt/ohm meter to find continuity break in points. And yes, they were bent to fit stacked on the piston, under the square.

I know it isn't as good as a dial indicator, but COULD it work?