Nearly every DSM vendor has bushings available for the shifter base to floor pan application.
I have the Energy Suspension two piece units, and they fit like a glove.
Also, you can use washers stacked up to the correct height, just be sure to measure them and keep the center tubes to maintain washer alignment.
Underdog/Tom shows that in his GVR4 restoration/spruce up videos on YT.
Biggest maintenance item would be to replace all the bushings in the pivots of the shifter arms, base, arms on the transaxle, and the little white nolothane puck for the up/down actuation of the trans gear selector rod at the top of the transaxle.
I had tons of play in the shifter pivot joints in the cabin, so I installed new bushings there; shifter never moved so smooth into gear.
Next I moved onto the transaxle side and swapped in good cable bracket spacer/bushings, nolothane puck, and lubed the arm that contains the copper bushings that actuated the white bushing; essentially your left and right movement on the shifter lever in cabin.
Without proper shifter timings, I had a biotch of a time shifting. Firstly my 4G shifter arm aligned my cable end hitting the base plate, but once clearanced, the only issues was all the slop in the remainder of the system. Why did I wait so long to do this!