Timing mark lies

[hound dog]

Have been running the cobra now for about 1,000 miles and I thought it ran pretty strong. A friend who helped me with the engine kept telling me "not strong enough". He kept telling me to "check the timing with top dead center". I told him he was full of $hit, the car ran fine and everything lines up on the torsional damper and the numbers say 10 degrees advance. Well, Friday night I took an old plug, removed the center and screwed a 3/8 ths bolt into it and left it protruding about 1 inch. I removed the other plugs and installed the plug with the bolt in it in number 1 cylinder (front on passenger side). Put some masking tape on the balancer, rotated the engine counterclockwise until the piston hit the plug and marked the timing pointer on the balancer. Rotated the engine the other way and marked the timing pointer again. Removed the plug and put the pointer halfway between the marks and removed the tape fully well expecting to see the TDC mark directly under the pointer. Couldn't believe my eyes, the pointer was about 30 degrees off!! I'd been running with the timing about 20 degrees retarded!! Reset everything to the new mark and 10 degree advance. Too much, detonation and engine wouldn't crank very well. I kept retarding until I got the engine to turn over properly when cranking and left it there. Car runs much stronger and no detonation. But now it shows about 10 degrees retarded off the new mark. I have no idea where my timing is now and I'd like to get it right. Anyone advise a next step? If I rotate the distributor a tooth would it put the mark back where it needs to be?
h dog