Ok well if the emulators sit like you say, I should order the 23.8mm YSS emulators and give them a crack (internal diam of SR forks is 23.95mm roughly).
I think this is the most promising direction yet, as you already have the fork brace.
After working on the forks on the black Jadus bike and the orange one, I would say preload would do a lot. There is so much sag in the fork already! I know that when you add preload you loose suspension travel. But the SR already has 140mm, which by today's standards is excessive for a road bike. I think if the result of a well sprung SR fork ended up being 100mm travel, it would be plenty.
I think I saved some info from CrazyPJ where he recommended Honda CB360/400F springs as they were a little loose for the Honda's 33mm forks and fit the SR250's 32mm (also mentioned XS250/400 springs). Probably could get custom springs wound but it would also be pricey.
See that is the thing with those plastic PVC spacers, it is trial and error and if you cut too short there is no going back. If I design the preload adjusters to have say 10mm preload in them already, they could have a further 30mm of adjustment travel and this would make a big difference. Then if the ride ends up being too harsh or oversprung, the adjusters could be backed out a little.
True, but PVC pipe is real cheap and easy to cut.
I know all the other paths to improve the forks involve larger, stronger/stiffer fork tubes and front end swaps, but call me old fashion, I just think modern forks look downright silly on vintage bikes. I know it's a fad right now and it is a taste thing, but the forks will always end up outperforming the bike. Besides, how many SR owners would be prepared to do a front end swap? Not many I think. I had a guy contact me on insta wanting to sell me a custom set he had made from Cognito Moto for 1500USD for his project. He of course had since abandoned the project and was looking to get some money back on the parts. 1500USD would get you an entire SR250!!! Mental imho.
Mental - agreed