First I took some measurements with pair of digital calipers, I can read a vernier scale but when digital calipers are so cheap why have anything else?
At high E, it was 5.26mm and low E 5.28mm. As a pure gamble I decided to lose about 0.2mm from the nut and see how it came out.
I filed the nut by holding it base down on the file and running it back and forth rather than holding the nut in a vice and moving the file. I figured I had more chance of keeping the base level this way. It took a while but eventually I got it to 5.03mm at high E and 5.07mm at low E.
Using a couple of replacement screws as I didn't want one breaking again I plonked it back on the nut shelf, restrung and set the intonation. Again.
The difference is amazing. It has gone from being tiring to play to lovely with just 0.2mm off the nut. Obviously intonation at low frets is much better too making it sound sweeter when playing chords that end of the neck. I kind of knew all this should be a consequence when I started but it's gratifying to feel the fruits of your labour first hand. So the RS8V has gone from being quite nasty to play to a lovely rock guitar. I can see me coming back to the RS8V to fit some different pickups but for now I'll move on to another project.
Half this job was adjusting the truss rod to take out the large amount of relief in the neck. I did this in stages, leaving it to settle and checking it as I went. Advice on how to check the relief if you're an amateur seems to be to fret a string at either end of the neck and look at the gap below it. This works fine, but is fiddly. Professionals probably have 'notched straightedges' but these are £45 from Stewmac and much as I like buying tools couldn't bring myself to splash out on a set.
So I made my own. I took an aluminium 19" rack blanking plate I had kicking around which was nice and straight, held it up to a neck, marked the fret positions with marker pen then filed it out with a round file. There is no way this is as good as something professionally made, but frankly it's good enough for me. One side is 24.75" scale length, the other 25.5", if I need something different I've got another blanking plate down in the cellar.