I'm with Dave up at the top. give me a timing light and a TDC tool of some sort and the timing will be spot on. Some hotrod motors run so rough at idle that it is hard to set the timing under the best of conditions. You have to set them at a point well after maximum advance. How do you know where this is?? If you have had use of a Sun Distributor machine and run distributors and with mag adaptor magnetos you will be able to find exact advance curves (if any) and be able to set the timing correctly and be prepared to make tuning adjustments.

Magnetos are set with a buzz box which works off the points and you can set them very accurately with these. For a long time it was the only way they were set. Today you can get timing lights that will work with mags.