Perhaps you could order a few sets from RSM and cut the recess in the top surface required for Mk.I and II fittings? Trouble is they are or should be, hardened after machining and you'd need to anneal them and then re-harden after the mods.

Twenty five or so years ago I had some 1 MOA plates made up by a very talented self-taught machinist for the purpose of making Mk.I scopes more user-friendly, but have only one set left kept as a sample.