The stock R20 has a SA 3 speed hub using a 112 wide hub. It's got a range of 185% (or thereabouts)
I'm thinking this is too narrow for a recumbent, particularly as I live on the slopes of a hill!
It's fairly standard practice in R20 circles to widen the rear drop outs to take a more modern 130mm hub
I actually have a NuVinci CVT hub fitted to my commuter minivelo at the moment and I'm thinking that that would make for a better gearing setup.
I'm hoping the mid drive will be easy as the R20 has a wide bottom bracket (76mm stock often narrowed to 68mm to fit modern bottom brackets).
This gives them a wide chain line. If I could use a standard double chain ring (with the pedal crank removed) and drive the rear wheel on the outer ring with the inner ring connected to the narrower spine bottom bracket I think I have a shot at getting it all to line up.
The connection between the spine and the rear half of the R20 will be slotted slightly to allow for adjustment of the pedal to mid drive chain.