I would think that if you take the bike to Draganfly Motorcycles at Bungay who make the Craven luggage range now, they will be able to measure and if necessary fabricate brackets to suit, as well as offer a choice of rack sizes and optional fittings for side panniers too.
I did this with my CB750 K2 in late 2019, and I know that they are trying to extend the range to cover more Japanese bikes. My bike features in their photos for the Honda range, if you want to see the end result.
In my case, the bike was ridden in, measured and ridden out. A couple of weeks later I went back for a trial fit prior to final finishing of components and the rack and fittings were then sent to me.
If you want to pursue this route, I could probably find the names of those staff that I dealt with, one of whom is ex-David Silver.