Where's the Wow?
I used the 10 degree BTDC mark on timing cover and I have degree tape on the balancer. So it hit the stop at 40 BTDC on the damper one way and 20 ATDC the other way at the same spot on the cover. If I need to use the degree wheel instead I will do that tomorrow.
I can't resist......
Sounds from this that the damper marks are 20 degrees off. If the OP referenced the 0 timing mark on the cover instead (which is 10 degrees CW from the 10 BTDC mark on the cover), that 0 timing cover mark would line up with the 50 BTDC mark on the damper tape at one end of the motion, and 10 ATDC at the other end of motion. With a 60 degree stop-to-stop range, then the zero mark on the damper tape would be 20 degrees further CCW than it should be.
That would put the crank 20 degrees further CW than true TDC when the damper mark 0 aligned to the timing cover 0. Ignition timing would then be 20 degrees retarded (a great cause for crappy performance). This should not effect cam timing IF the chain set is set dot-to-dot AND the sprockets and crank keyway are machined right (as it would be impossible to get the crank sprocket dot straight up). So the damper marks being off will throw off ignition timing...and be useless for cam timing. Get this: Damper marks are not intended for cam timing. They don't possibly cover the range needed for finding ICL for example.
At this point, the OP should be using the piston stop to:
1) Check crank keyway and sprockets being right or wrong and find true TDC. At the middle of the stop-to-stop range (forget the actual damper or degree wheel readings, just get to the exact center of the stop-to-stop range), then a correctly machined crank sprocket dot should be perfectly straight up and lined up on a line from the crank centerline to the cam centerline.
2) Then at that crank position, find where the 0 mark on the damper lines up to the timing cover and note that particular timing cover mark as the reference point for ignition timing in the future.
THEN the degree wheel gets used to set up cam timing.