I recently had a similar problem with my Ford GPW. I went for a 25 mile run and it never missed a beat, switched off for ten minutes and it refused to start ! I replaced condenser, points, rotor arm and cap at roadside and she fired up, problem solved or so I thought However nearing home she started missing and struggled the last mile before dying again. I replaced the coil with a new one and all now seems fine. I believe the coil was breaking down once warm (hence it restarting when it had cooled down), and talking to the local classic car garage they have seen the same many times.