Thought I would provide an update on the caster story. Thanks for the input from Barnett and also Justang and Kerry.
Because I wanted to do the shims with the UCA still in the car it was not possible to remove the bolts. By using stands to take the weight of the car I was able to separate the UCA balljoint and drop the weight off the UCA which allowed me to put shims in. I used cone lock nuts and removed the washers on the front bolts while leaving the rear bolts as standard. I was able to put 8mm of shims on each UCA then used loctite on the cone locknuts.
Pretty easy job in reality.
I now have between 5 and 5.5 degrees caster - up from about 2 deg previously. The vehicle is more settled on the road and a little heavier - or less light- in the steering. The power steering has always made the steering a little light and floaty, almost overdriven by the power steering pump which is common apparently.
I left the tube on the strut rod as I have poly bushing on the rod but might look at doing this in the future if the bushings fail.