This could help Gargoyle Reviews
The bushings are smooth delrin that goes between the barrel and the pump handle, they help to smooth out the pump stroke.
Body is AC threaded and the adaptor which is I believe .69 (Dimples are basicly widgets and are standard go to about .679) allows use of the Phantom stock barrel (.686) which is one of the best stock barrels ever (the best single piece stock barrel IMHO)
Nelson or AC springs will work, it comes with CCI Nelson springs.
Efficiency info can be found in the link above.