To the best of my knowledge, none of the SM-420 Synchonized four-speeds had a pinky-lever.
To get the synchro into "Reverse", you push down on the shift lever, pull it toward your leg (to the left), then back toward the seat.
I've seen the pinky lever only on four-speed crash boxes (necessary because "Reverse" and "Second" are right next to one another). 3-speed floor-shift crah boxes don't have a pinky-lever.
BTW: the official name for the pinky lever is "Reverse Lock-out lever".
My '48 IHC four-speed did not have a pinky-lever; my '34 IHC four-speed did...
I would be surprised if GM offered the new synchro-4-speed in the old Art-Deco trucks...I think the bolt pattern at the bell housing might be different ?
