I would like some info on master cylinders. Do they differ from drum front to disc front?

drum ones used to have residual pressure valves in them but these days when you buy a dual circuit MC, which yours shoulda had from the factory, then there appears to be just the one variety available for sale from what I've seen.

The residual pressure was meant to help keep the shoes closer to the drum at the cylinder end of the shoes.

Okay, Thanks for that. Now if i want to change to discs it sounds like i will have to remove the valve if possible or replace the whole thing

Give Vintage Vee Dub Supplies a call. They have done many conversions and will give you the correct advice.