Your title ''just'' says,, - Model ''P''.
As far as converting to disc brakes, I don't see any feasible way to do it with your rims,, as there is nothing to bolt rotors to..
Am thinking you would have to come up with a different rim/ rims that would fit that,, with them having mounting holes for the rotor/ rotors ect.
You would probably have to have caliper mountings made up & welded also.
Personally,, I would just take what you have, & scuff up the band/shoes & drum faces,, with like 80 grit sand paper,,,& see if that helps it stop better.
Brakes are probably just all glazed up,, as long as the bands have meat left.
Generally you would measure contact face diameter, plus width,, for band/shoe size.
I wouldn't butcher that.
Have your 11 year old Grandson help you with it,, then he will know how to work on it,,, & also understand how it all works.
I was tinkering around mechanical stuff even before I was 10.
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