I'm taking a different approach with the big GMC 3 ton that's going to be an upcoming project. I'll stick with the SM420 main biox, and add a 3 speed Brownie in the same place where the center driveline carrier bearing is located currently. That setup, along with the vacuum shift 2 speed rear axle, will give me 24 forward speeds- - - - -and six in reverse! That should keep the 270 engine humming along in its happy place RPM no matter what the terrain happens to be! Plus- - - -it's been a long time since I've had two shifters and an axle splitter valve to play with!
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!