Well that was an interesting little job for someone with cowman sized hands!!!!
Following John's tip that you could (just about) remove the adjuster without taking off the gearbox cover I had a go this morning because, as you will see in the photo below, the adjuster was far from parallel with the arm.
With the aid of a magnet as part of the operation (retrieving parts as they dropped into the gearbox and holding the nut as I attempted to start it back on the threads) all is now well.
I was sort of lucky in the the PO hadn't put in a split pin so that was one less operation in the dismantlement.
It wasn't possible to get the adjuster totally parallel with the arm as the splines weren't positioned kindly for me - but it is a lot better than it was!
Getting the nut back on was a challenge as was lining up the split pin hole with the nut castellations. However, a whole lot easier, quicker and cleaner than taking the gearbox cover off.
I then took a deep breath, measured the SRM small pushrod and chopped the equivalent length off the original pushrod. I have just stopped for lunch and to re-read the instructions before adjusting it all up and hoping I got the pushrod length right
Brian