I own a rapman (bits from bytes laser cut reprap derivative) and looking at many designs I like the extruder this guys made very much. The extruder is divided in two parts (linked with 2 screws) - the "drive" part where a stepper driven shaft grab and push the filament - and the "hot end" part that is, well, melting the plastic.
After many kg's of filament (abs, pp, hdpe, pla) trough the hot end from bfb I never had issues with it and as they sold hot end as a separate "part" I figure one can mount it to the Mendel using the pinch wheel drive and the bowden cable as the "other part" of the extruder assembly. This is a good idea but a hot end from bfb is ~40mm in dia hence I had to modify the carriage a bit (just drilled a big 40mm hole in them).
- print lower carriage
- print upper carriage
assemble as defined in mendel manual
put the hot end trough the hole
attach the "bowden cable holder" to the carriage and attach the bfb hot end to the holder (this part is still being drawn)