Hi Carl-Erik,
I used both ways you mentioned and they really work well in the past. Good tips.
The problem I see with old cases of the 20s is that they don't have the timing hole like the late 30s ones.
OK, you can use the hole of the handpump elbow or the oil level plug, but they are a little to small or difficult to reach.
I really like to insert a 3/4-24 UNS thread inside the case to use later Indian standard timing hole plugs.
Asuming you have already marked the flywheels TDC during assembly (preferably on both cylinders) you can then flash the ignition point with a transparent plug and a ignition timing light that has an advanced timing wheel.
I know it's not original, but when done well it's hardly noticeable and checking the ignition timing and possible misalignments between the cylinders is a matter of minutes.
I think, when you want to have an engine as fast and reliable as possible, you need a way to check the timing with an ignition pilot light gun to eliminate or consider all play in the gears and in the magneto (or distributor).
