Fantastic replies gents thankyou - i'll investigate a bit more tomorrow.

The original parts have the Mikuni QC stamp. I have removed all Keyster items, only using their float valve and reading around the forums I will not be using them going forward, even if this time I just ordered the wrong thing!

If your original bowl gasket is not torn, it's safe to reuse it.  Original gaskets are very good.  If carb has been dry a while it might seep but that will quickly stop.  New gaskets sometimes do this too.  O-ring that seals to float bowl is the critical part. 

Yep just replace 'that' Oring & clean up everything else & it'll be good.

I've put her all back to stock and been for a little road test; what a great little bike!

first time I've ridden her since importing it and even though I've got some issues I can understand it all now, what a simple to ride and fun little bike!

Just ordered new clutch plates and springs as my clutch is slipping really badly. Tried adjusting as per service manual but unfortunately still slipping. It'll get there!

as for the carb - I'll watch some YouTube about mixture screws in two strokes - I can't tell much difference when playing with it whilst it idles. Will also keep my eye out for a CT1C carb with the vertical choke, this will make jetting and fine tuning a little easier I believe as it it's a known quantity vs my mystery carb!