I still have points and have always used the cigarette paper in the points trick.
With the points timing cam set in the advanced position the engine is turned using the back wheel so the paper just releases. ie the points just begining to open. this should be the 28btdc. Adjust the points backplate until its right. then do the same with the second set of points this time adjust the points plate until its correct. Make sure point gap is also correct as this will affect the opening position.
Recheck with decent timing light if you have one.
I intend setting the timing up this weekend if I get the chance. Before I start i want to make sure that my timing graduation marker is in the right position because i removed the primary front & rear cases and found the centre spindle loose. So after tightening it all up it could be its moved position?