49 geezer,
I made a little cartoon of the impending surgery, and it looks tenuous. This would depend on how much shorter you are making the shift arm of course.
You must achieve the amount of travel the detents in the side cover require..that's a given. When you shorten the arms on the column mounted shifter box, you will have to move the
shift lever in the cab more to satisfy the detents.
If you are making those levers quite a bit shorter, I think I would pencil it out first. You might not have enough travel inside the little "H" box on the steering column.
Hope I got my geometry right!
Stuart