sounds good.. Resist any temptation to do any more piston sizing; just shoot 2 or 3 dozen, then rough tune the spring spacing... it'll probably wear in and creep up a bit more, but most of the wear will come very quickly. Certainly by the time you have shot 1/2 a tin, it'll be completely settled / worn in .
Are you using the original MK3 spring still ? And have you kept the large and excessively heavy steel piston weight / top hat (you can see where this is going) ?
Always looking for any cheap, interesting, knackered "project" guns. Thanks, JB.