1 & 3 look like they may have been taken just before Ginger Hall.  2 is from Creg Ny Baa and is a 125.  Looks like an expansion chamber coming out from the fairing, so a 2 stroke - maybe a BSA Bantam.  No idea on any of the riders though.  Needs someone with a programme!  They helmet design on 1 looks a bit like Gyula Marsovsky but I would have thought he'd have a higher start number.