'three on the tree' sticking in reverse = confused Brit!

[disasterbus]

I’ve got a 1964 C-10 with factory standard inline 6 engine and 3 speed column change gear box – the stock ‘three on the tree’.
It has now developed a problem where it gets stuck in reverse gear. The only way to get it out of gear is to open the hood and manually pull or push the selector rods to de-select reverse and get it back into neutral. It has only just started doing this and it only seems to be reverse that this happens with.
I recently replaced the steering wheel and boss with a Mooneyes one, that’s the only work I’ve done on the steering column (or anywhere near it).
Any suggestions what the problem could be or how to fix it?
I’ve taken some photos of the selector mechanism and how it lines up in each gear. Does it look ok to you guys or is there something obviously wrong?

First 2 pics are with the shifter in neutral



The next 2 are the shifter is first gear



The shifter in second


These are the shifter in third gear



And these 2 pics are with the shifter in reverse



Really keen to get this sorted as I had planned a road trip next weekend to Grizz and Martin so us Limeys could work on our trucks together - yes Rian, I know you’re not a real Limey, just an adopted one! ;-)