What happened to the air gun a guy on here was making, not seen any updates lately. Atb mick
The best method to fit a breech bolt is to drill and tap 10mm through the pivet hole ,make two bushes from a 10mm bolt and glue and screw them in .
If I remember correctly, the Meteor tube is 25mm and the Mercury is 28mm, so you'll have to shorten the bolt and maybe tap the thread a bit longer, not really much of a problem, I suppose the other way of doing it with hollow forks would be with the Diana 34 set up with the correct size tube and then the two bolt arrangement, at least it would have a solid area and wouldn't damage the forks if you tightened them up to much.
Pete
Far too many rifles to list now, all mainly British but the odd pesky foreigner has snuck in