There are a few that are already building them. TKO22.com, Pacific Pellet guns and Mountain Custom Airguns. All 3 offer variations and will build you just about any configuration that you want.
I have shot personally a TK022 conversion with 14 inch barrel. Shot VERY well, trigger was really good. I have one on order from Darren at Pacific Pellet guns. I ordered myself an all Stainless gun. Cant wait to get it... He has built some nice ones... Search around on the yellow. Here is one from Darren: http://www.network54.com/Forum/79537/thread/1250538335/A+big+thanks+to+Darren+at+Pacific+Pellet+Guns-
another resource to see many PCP conversions.