Just got an email from Ken yesterday also letting me know that my Systema PTW arrived.
Final payments were made and the gun should be in the post by now. I should have it early next week... w00t.
Propane adapter? How about going direct to the manufacturer (Our very own MadMax)? http://www.airsoft-innovations.com/
Future upgrades: Metal slide, enhanced recoil spring, enhanced hammer spring. I can order them all for you if you need, as well as the various other guys out there who run group orders.