Slant got me stumped
nm9, After thinking on the drive home...When I changed the chain, I lined up the timing marks and installed the cover. I remember the balancer mark being as you said about 15 degree's before and I shrugged and rotated the engine around with my finger in cylinder 1 until I felt pressure build after the intake circled around and then brought it to TDC on the balancer....
Well the damper mark should have been 15 degrees AFTER the 0 mark (towards the driver's side), not BEFORE, if everything is right. On the /6 timing scale, 15 degrees AFTER is not even on the scale markings; the scale usually runs maybe 5 degrees AFTER to 15 degrees BEFORE. So if you saw the damper mark at the 15 degree mark, it can only be 15 degrees BEFORE........
So if the dots were really lined up right and the damper mark was at 15 degrees BEFORE, then it sounds like the damper is about 30 degrees too far advanced and is showing far more advanced timing than it actually is. All this is based on what you are telling us of course.....but it could sure would explain why you need what looks to be so much excessively advanced timing....
Soooo, that gets me back to thinking if it was me, I very soon would take the time to check the damper mark versus true TDC, and not be 2nd guessing myself. And I'd also look very carefully at cam (valve) timing versus true TDC. When you actually do find TDC, the intake and exhausts on #1 or #6 should be about equally open. (This is just a rough method; just a check before tearing the cover off.... which I agree would suck.)
Trying to find true TDC with you finger in the hole is a good way to be off by 20-30 degrees either way; please don't waste your time or ours. Use a solid stop; it is not hard to make with a spark plug if you break/drill out the guts and thread the inside for a long carriage bolt, and use that to carefully find TDC. The pencil method is too rough also, when one is trying to really get the damper mark nailed within 1-2 degrees. The piston motion is very small per crank degree near TDC or BDC.
Other possibilities still remain, and I would also keep on those (LIKE CHECKING SPARK STRENGTH AND TAKING VACUUM NUMBERS; THOSE ARE FUNDAMENTAL TESTS THAT SHOULD HAVE BEEN DONE ALREADY..... which makes this a great statement: "In 73' they are kind of still very basic. After 25years of turning wrenches for a living ALWAYS go back to the basics.") But from your symptoms, this damper mark issue needs addressing. Personally, I would do the checks on the present damper so I would know waht is actually going on before getting a new damper. Of course, if you have another damper, it would not be much effort to compare the 2 as a start.