Cory, thanks for clearing up the interference issues. I wound up rebuilding my SM420 and keep the entire drivetrain (except the 235 engine) original, but that's more because my plan for the finished vehicle has changed... I want it to be close to the real thing, just safer and more reliable.
I drove my truck around town with a transmission that had bad syncros and I couldn't downshift into second. That 216 would pull that truck up from like 15-20 mph in third gear without a shudder. For someone like me who grew up on 3-speeds with no syncro in first, driving a fully syncro 3-speed is a luxury.
It just depends on your personal preference and I like my truck to be an old truck... with power disk brakes
