Richard,
Glad to be of help, after all, that's what we are here for, to help each other.
Phil, Never thought about using a vac gauge, good idea. I'll store that idea away for another day. If you happen to have a spare camshaft lying around, you can see how the rule of 13 works ( it also works on a 4 cylinder in line engine as well, only you follow the rule of 9 !)
Trouble is, that most modern mechanics would not know how to adjust tappets, let alone dwell angles and point settings !
Regards
Keith