After some more testing, setting the lens to infinity then unscrewing it from the adapter a little bit at a time I'm getting it sharper.
So I may just have to make some paper/aluminium shims to sit the lens further away from the sensor
Makes me think, maybe one of the previous owners added shims internally for their camera (as I'm sure I've read about people using the same lens on their R D1's).
Once I get it sharp with external shims I'll check to see if it fixes the coupling too'
This is the gap needed to take sharp photos at infinity:
So made a carboard shim, now it focuses at infinity, at minimum focus distance and the coupling seems to work fine now.
I guess next step will be to take apart the lens and find out how to shim it out internally. Not too happy with carboard shims on the outside (flimsy, rather not have the lens hanging off not completely threaded on, and with the "external" shims all the markings are on the bottom of the lens).
Scratch that- now infinity works but minimum is off ): So confusingggg