The earlier d20 transfer cases used in Scout 800 (along with many other vehicles!) were a twin stick-controlled unit.
And any single stick control d20 May certainly be converted to twin stick operation, very common (I have some of each type). We have a twin stick conversion shifter on the shelf now, but it's not a simple matter to just bolt that on! The interlock "pills" on the single stick d20 must be removed, but you must retain the detent spings and balls in order to keep the various shifter positions "locked" in place. Jumping out of engagement is a common issue with these cases if the springs are weak or the detent balls (and the rails) are worn beyond limits.
Here is a quickee scan right out of the early Scout II service manual (cts 2304) that shows the shift pattern for the oem twin stick units and the later single stick with an explanation of how the single stick interlock operates.