Installed reman carb today and went to adjust timing back to stock, currently 12 degrees BTC and should be 4 degrees BTC, but alas no timing marker on block. All that's left are 3 holes. Haven' checked to see which are threaded yet.

Is there a way to know where the timing is set without the tab? Or am I looking for one?

 

You should probably get an aftermarket add on timing tab. Then rotate the engine around to TDC #1 (feel through the spark plug hole with a piece of solid wire for when the cylinder tops out and starts to go back down. Align the new timing tab with the mark on the crank. Highlight the mark on the crank with some white chalk and time away!