The Chinese 139QMB and the Taiwan KG10SA are interchangeable engines, except for one mud-guard trim fitting. I replaced my KG10SA with a mail-order 139QMB a few years ago, added a BBK and cam, adapted a mail-order exhaust, and it's still running fine. The exhaust can be a fiddle since the fittings may not line up. This is normal - take it to a local muffler shop for adjustment.
Thanks for that info, Its great to know. When my engine finally gives up the ghost, I know what I can replace it with now
I got the Stage6 exhaust in the end, It fits nicely, Looks like it was supposed to be there standard. Removeable/reinstallable baffle is nice to have too.