Thanks to one and all for the advice and comments - vitally important to a newby BSA owner. This morning I checked the end float using a DTI and am content that the resultant figure of 0.019" end play is accurate. I then removed the main bearing and found a ragged 0.002"shim sticking out, part of which must have gone elsewhere, together with a 0.010" shim in situ so the total shimming needs to be in the order of 0.030. I'm going to see if I can make a one piece spacer so that I can eliminate the need for multiple shims. Valves etc are on my list of "things to order" today!