Dave, dont forget that the accurate way of finding TDC it to remove no.1 spark plug and rest a 8 - 12 mm steel/alloy *rod on the piston crown, then rotate the crank/pulley assembly slowly until the rod is at the highest point.....

In fact the rod stays at this highest point for a few degrees (known as dwell) TDC is at the middde of the dwell point.

* or a long screwdriver can be used.

Doug.