I was in the process of reassembling my long disassembled '75 Norton 850 and found that one of the rocker spindles was a sliding fit in the ol' RH4 head. Another one was almost as loose. They're supposed to be more of an interference fit to the point you need to heat the head to get them installed. Among the host of issues that loose spindles can cause is allowing the spindle to rotate (it's supposed to be held in position by an absolutely poorly designed stop plate) and will allow a lot more oil to enter the rocker cavity. This, in turn, swamps the valve guides allowing oil to get sucked in and burned which results in massive amounts of smoke and plug fouling.
One of the better fixes is sold by RGM in England (https://www.rgmnorton.co.uk/buy/one-piece-rocker-spindle-locating-plate_4062.htm). It solves two problems actually, it'll keep the spindle from rotating, and it allows you to really lock it in place with the grub screw which should help keep it much more stable over the long run.
Since I am impatient, had some stainless bar and a CNC mill, I decided to whip up my own version of these. I think they came out pretty good.
And here's the final result. I think they're going to work very well.