Parts compatibility

I've done a search here and elsewhere to find answers to some questions I have. I've decided to revisit some of the work I did a while ago on my ex Alan Keane racer. Alan owned it from 1971 but it was a year old when he got it. It already had a 125 top end but I now suspect it still has a 75cc gearbox (see wanted section!) One of the areas I was never too happy with was play at the mag end of the crank. My mag flange is marked 20.05.0014. What type is this? Roller or ball bearing ? Single or double oil seal? Are the bearings available. Is it the type you used to be able to buy as a complete assembly?
What I'm planning on doing is curing the slop in the crank and likewise on the layshaft/rear wheel bearing. Reboring, it already has a 57+mm piston (can't remember how much bigger) and sorting out the lighting issue that cropped up the other night on my way back from a local scooter meet. I'm determined to get this as mechanically sound to compliment the rest of the restoration.

Paul

paul, both types of mag bearings can be bought, so thats a good start.
i know that its possible to use a tv175 piston in a j range motor, but it leaves the skirt of the barell very thin.

Thanks Daz. I spoke with Jem B yesterday and I've decided to have him work his magic on the engine. Although I like doing my own work it seems practical in the long run to drop it into him on my way up North to visit friends.

Paul