A904: 1-2 shift happens early despite governor weight- any way to adjust this?

The factory kickdown linkage was sloppy at best when new let alone now 45 to 55 yrs. later.
Since you do not want to go back into trans. Recommend a lokar kickdown cable & throttle cable combination. Relatively inexpensive and easy to install and adjust. Will insure you have kickdown all the way back at WOT and all the way forward at idle without slop.
Lokar throttle cable will help guarantee you are consistently absolutely at WOT to maximize kickdown performance