I have three Cooper-T Imp kits for Sheridans. This allows you to convert a Sheridan pump into a semi. I have seen a few of these conversions and they are interesting to say the least.
The kit uses the original trigger frame, but the original bolt is replaced with the delrin bolt supplied with the kit. The brass insert with the valve on it and the hammer replace the original hammer and valve. The original valve stem is still used The kit with the white bolt uses the brass sleeve with a hammer, but retains the original valve and valve stem.
All three kits work best with a Sheridan originally set-up with a BB adapter. Since these are already side tapped it makes it a little easier to adapt the Cooper-T kit. You can also modify other Sheridans with a little more work.
Asking $85/ea shipped.
Here are some pics:
Top Two Kits SOLD 
I accept Paypal or money orders. Paypal addy is
pbmaniac@sbcglobal.net.
Let me know if you have any questions by sending me a PM.
Thanks for looking.