Having decided I was happy with the paint finish on the RT-320, and having mostly rebuilt the radio into the front panel, I managed over the last few days to complete the rebuild of the ATU, and put the radio on test...
Bugger! It seems that although the coupler for the turret tuner can only fit to the tuner in one way, the control shaft can fit to the coupler the wrong way around!
I now have a radio where the band select knob points 180 degrees opposite to the selected band!
So, it looks like i'll be dismantling it again. Hopefully I can get away with just releasing the turret unit enough to turn the knob around!