Would it be possible to use the ball end of the torque tube that fits your bearing retainer on the existing torque tube? Just a wild guess, but I'll bet the SM 420 used a different ball than the 3 speed. I've got a 51 GMC frame stashed away that had a 420 in it and the torque tube is still there. I'll get some photos and measurements as soon as I get back from a trip to Nashville.
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!