Dampner out of wack

You can do this either way. You can even find degree wheel photos on the www, and print them out, and glue them to a disc and make one

The thing is...........I doubt you can buy a degree wheel locally

The MAIN thing is to be careful, use patience, and double check your results. "Draw it out" if necessary.

If you use the stop, and the stop is "SOLID" that is, does not move, you will have very very little error, within one degree, certainly.

In a V8, the piston pistons are offset from the center line of the piston, so this adds some error when using a piston stop---but certainly not as much as a degree.

Now in your last check, "about how far" from TDC were your two outer (temporary) marks? I would say at least 15--20 degrees would be good. If not, make a longer plunger for your stop device.

Once again, it is important to add a lock nut to the stop and to get it snug in the plug hole, to prevent the stop from moving.