On these mopars, there are no numbers on the balancer. There is a notch / line in the balancer. That’s the top dead center mark. You should have the timing tab on your timing cover... passenger side.. as kryslerkid posted.
Here’s what I’d do:
1) find the mark on the balancer, clean it off real good and mark it with a dot of whiteout.
2) Clean the timing tab real good and mark the 0, +10 and -10 with white out. Your timing tab should have a line for 0* clearly labeled (some also have a hole on the zero line). There should be two or three lines in each direction, these are in 5° increments. Most timing tabs have the +10 in -10 clearly labeled.
3) mark the base of your distributor and make a corresponding mark on the engine block - so you can always return to your initial setting
4) loosen your distributor - not dead loose - just loose enough that you can twist the distributor with a little force.
5) start the car and check timing - should be in the neighborhood of 12 - 14 degrees advanced at idle. If it isn’t, twist the distributor until it is, then lock her down.
Don’t set your timing with vacuum. Doesn’t work in my humble opinion and will have you way way advanced.
———— Edit:
Here’s a pic of an aftermarket timing cover I have - timing marks are a little different - I think these are the 70’s timing marks.. your 68 should just have -10 through +15 I think.
wish I had my old 383 damper, but “she gone”. I’d have shown you how it all works together...
But once you find the marks l, even I can do it.