Appreciate this insnt a beesa preunit singles forum, the damn things are typically too reliable to need one
Yes typically the mag is 1st point of attention, take the plug out, hold it against the head and do you get a nice big fat spark?
Also put your finger over the plug ole and confirm you've got compression, if not tappets might be tight or you new valve seat not sealing (so not sucking the juice through).
I owned an M, great bikes, tough as old boots, especially the pre 48 girder jobs.
keep us informed and please post a picture of the bike.