transmission surgery?

Hi all,
I have a 72 Commando and the transmission is acting strange with false neutrals and popping out of gear a bit and odd feeling first gear selection.
I suppose I will have to go into the tranny and the description in the workshop manual looks pretty straight forward.
Any words of advice?

The spring fork in the outer cover selector mechanism may be the culprit. Also replace the layshaft bearing with a roller equivalent. The original ball was prone to failure. See the Old Britts web site for excellent guide to overhauling the box.

Mick