Hi Jimg, so sorry for a slow response to your questions.
firstly my bike isn’t a jumbo, it’s an 83 TL320. Rest assured the shorter springs won’t cause slip on your 350. At the end of the day both 240,280 and 350 are downrated mx engines that would need the strong springs for that application and furthermore theyd be clutch less shifted so a heavy clutch wouldn’t be noticeable. I think 340mm is the stock shock length but I run rockshocks 360mm with no noticeable difference, if anything you gain a tad more travel when the bike is weighted. I also swapped the well tired fork springs for a pair from REH, a hard one in one leg and a medium in the other, they are shorter than the originals by about 20mm but a longer spacer solves this. As long as the springs are longer than the travel your fine. I recently rebuilt the engine and fitted a clutch hub off an Aprilia TX311, this has the last plate as part of the casting so uses one driven plate less than the SWM clutch and has a far superior actuator bearing. I get no drag at all with this set up even if the bike is stood for a while. If you go down this route just make sure you get the 3mm thrust washer that fits under the splined tab washer, the SWM uses a 1.5mm thrust washer with the standard set up. Hope there’s some useful info for you all.
