Timing cover off old sbc fits just fine on vortec. Two bolts are not drilled but have the boss cast in it so not a issue if you want to drill them or use some silicone. I have drilled 4 or 5 so far and left a couple without drilling and never leaked.
Edit..... wouldn't use one that didn't have a crank sensor in it unless using a external crank trigger or going carb.
Edit..... wouldn't use one that didn't have a crank sensor in it unless using a external crank trigger or going carb.