The original trunion had come out of position, allowing the shift linkage to travel against the left inner wheel arch when selecting first. I had a new billet aluminium trunion that I bought a few years ago from PIM (http://www.pim.net/tpage.html)so put it to good use.
However having noticed the stress shifting puts on the trunion I can also see why a cable conversion improves the gear shift, as it removes a significant friction point. Having said that though I actually have the gears shifting pretty nicely now.
Took the opportunity to take out the entire shift linkage, clean and regrease. Also regreased inside the shifter box whilst I was at it.
When for nice drive and shifted perfectly.
Happy days.
I was actually a bit weary of stuffing something up as I haven't played with the shift linkage previously, but having had this experience really helps to make clearer what others are talking about in other posts.
Jack,
I also looked for the two screws that are meant to be located on the underside of the shifter box, but I don't have them. I'll post some pics soon.