I think the M type ali cap strip is 32mm half round, the same as used on the D, F and J1. In the UK vintagecarparts.co.uk supply it, but if you only need a door cap I'm sure I could find enough to bring to Stoneleigh.
I have not been able to locate my spare door cap strip. I have found the front tub strip, but those strips that were on the doors are no where to be found. I will continue to look, and let you know.....
Still have not been able to locate them...... better look elsewhere if you need them in a hurry. Perhaps they will turn up during sring cleaning.. So sorry....