This extruder is a great improvement for your Replicator-type closed extruder! It has been remixed from the direct replacement (original was set up for a smooth bearing and a hobbed feeder) to fit the FolgerTech Prusa i3 (or any other that has a v-groove bearing and a flat feeder).
I have also added a small finger rest to serve as a leverage point. This solves two problems with the original design 9as installed on my printer): No more accidentally pinching the hot end mounting block (ouch!) or putting downward pressure on the X-carriage when changing filament.
STL files are included for left-hand models (as equipped on FolgerTech Prusa i3) or right-hand models. You can also print both for use in dual extruder setups.
The installation uses the following heardware:
1x grooved bearing (from your old extruder)
1x M3x5 (or a bit longer) countersink screw to mount the extruder to your stepper
1x M3x10 countersink screw to mount the bearing
1x M3x20 (or a bit longer) to mount the lever to the base/stepper
1x 8mm diameter compression spring to provide tension
The spring is available in a kit from Home Depot. You'll need to cut about 1/4 of it off.