There were three different damper lines and timing tab combos
used on the Gen1 SBC.
will allow you to be sure the timing tab and damper are correctly indicating TDC. If they're not, the timing can look whacked and you'll not know if the total timing is correct. And if the total timing is too high the engine can detonate, and that can kill it dead.
MAKE A TIMING TAPE
to see what the total timing is, w/o needing to use a dial back timing light. You can also buy a timing tape, get one that matches the diameter of your damper.
If the cam is big enough you'll need a lot of initial. Give it what it wants. Limit the mechanical so the total stays where it should be- about 36-38 degrees BTDC at 3000 RPM or less for most iron heads, less for fast burn and some aluminum heads.
If you're geared to turn less RPM than where the timing is all in by, and if this is often street driven, use a vacuum advance set up to give 10 degrees timing under light throttle cruise conditions. If the initial timing is over 18-20 degrees, try the vacuum advance hooked up to a ported vacuum source.