Don't get greedy on the OD ratio! I've seen the two transmissions on one of those Rube Goldberg rigs close-coupled by using two slip yokes and a single universal joint cross. Getting the input shaft coupled to the driveshaft takes some pretty creative maching, but it is doable for a determined tinkerer!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!