New Carb options are available now, brand new PWK's and so on if I interpret correctly.
I just read a bit of UK magazine "Classic Bike" and Fahron engineering seem to be able to convert 250 barrels into not just 350 barrels but have other options. Relinining and so on. Not sure of that detail but this outfit are pukka engineers so I would not be surprised.
Fahron have been around as long as Stan Stephens, they're legends. They produced what was a very famous liquid cooled complete top end for the RD400 air cooled's way back in the day.
I think I shall investigate and put up a summary
Wondering if there's enough meat on a 250 head for a tuner to convert it into a 350 head.
Main reason I mention it is that so many RD's and RZ's here are 250's, so therfore are the available spare parts. Got to say it, that extra 100cc makes the motors a lot more useful.