Could you folks help me determine...

[Fitz]

Sounds like you have several problems. A stuck lifter will tap and , since it is opening and closing a valve, your vacuum meter would dance in time with the tap. Good way to find out if it's a lifter is take a long screwdriver, put the screw end against the valve cover and your ear on the handle end. Try this in several places and stop where the tap is loudest.

Since it smoked when you started it after laying up for a while AND you have low compression on two cyls (but not too low) you might have worn or incorrectly installed valve guides on those two cylinders.
Installing an HEI wouldn't hurt, either but I suspect it'll be mo-bettah to fix the other stuff before going that way....just an opinion.