Gotta do the math before moving on the third rotation
My math keeps coming up around 3 to 4 degrees BTDC. 13+20 = 33 33/2=16 degrees. Take 16 from 13 and you get 3 degrees BTDC. Take 16 degrees away from 20 and that will leave you with 4 degrees BTDC. So in between 3 and 4 should be true TDC if your numbers were right. Could measure it with a tape measure (thank a tailor tape) from your measurements, then just divide that by half. Another easy way, lay down a piece of paper on the HB, make a mark with a sharpie on the paper corresponding with your 2 readings. Now just simply fold the paper until the 2 sharpie marks on the paper are alligned evenly. The crease fold will be exactly halfway between the 2 marks. It isnt real uncommon for the TDC mark to be off by a few degrees.
Now we're talking!!!
But his heads are bolted down.....he could use long cigarettes through the sparkplug holes?