This discussion should include consideration of the following:
These guys have by now gained considerable experience and insight into chain redrive in an ultralight aircraft application.
Seems to me that if a chain drive were suitable, its housing could be made out of a short length of extruded rectangular cross section aluminum tubing, say 2"T X 6"W X 12" H, with, say, automotive timing chain and gears from, say, a BMW 3.5L car engine, of which I have several. One such was removed with its sprockets from a 3,500 lb. car after 300K+ miles, still in good shape.
Also useful may be the BMW guide rail and chain tensioner bits, and all parts would fit inside the 2X6 extruded aluminum tube, with an oil bath at the bottom such that the chain constantly runs through and flays oil around dissipating heat to the aluminum walls, so add a sealed cap to each end of the tube.