Brother-bee, when you start fooling with the shift-shaft trunnion, there are a number of clearance areas you need to watch simultaneously. There's a channel in the left motormount that the shift rod slides through with little clearance, and an adjustment coupler that gets very close to the edge of the inner rear fender on one side and the bellhousing on the other. Plus, when the height of the trunnion is changed very much, the total length of the dog-legged shift-shaft also changes, which can cause popping out of gear if some are selected. These maladies can accompany a bad rubber isolator in a motormount, too, making diagnosis complicated.
If the trunnion is loose of course, you really have no choice but to adjust it, and the length change can be adjusted for quite a bit using the splined end of the last u-joint rather than loosening the big adjuster. On our car, I was never able to loosen that adjuster- it takes ZF removal to get big enough wrenches in there, and so far, I've always forgotten when the box was out. Finally, if you have one, be very careful with the popular aftermarket aluminum-and-teflon trunnions. That area gets awful hot while running and teflon softens at low temperatures. The teflon bushing sometimes softens enough to slide past its setscrew and out of position, suddenly making shifting very difficult. Very hard to repair on the road with a smoking-hot engine.