DaddyCool
To the best of my thinking, I could get say a Federal female freecoaster with 10mm bolts - in order to to fit it into 3/8 dropouts I'd basically be cutting a slice off the very ends of the 14mm central axle and allowing the dropouts to fit around the bolts directly. I guess the danger then would be damaging the threads?
I have heard about slotted axles and thought about that possibility. I reckon using a freecoaster with a solid 14mm axle (not hollow) would be best for this, and the only freecoaster I know with a solid 14mm axle is the Shadow one. I'm not a mechanic, so I may be wrong on this stuff.