I would have to disagree with you there. I have got 4 original OEM Ohlins MX6 sets and they all are exactly 400mm eye to eye. I even checked the workshop manual and it says 400mm too. I cant remember the exact stroke but im pretty sure its 145 or 147mm (metal to metal) with old body cap and 3mm less with the new 6 mm heigh body cap. I can check for you if its criticle.
Just checked my notes and i have measured 145mm for stroke and manual says collapsed length is 256mm so if thats taken off 400mm stroke is 144mm acording to the manual. Thats with the old caps.
As I understand it the steel swing arm 250MX6 originally had the orange S&W shocks, 'though the 400s may have had Ohlins as an option. The S&Ws measure 408mm centre to centre at full extension, and 270mm compressed against the rubber stops. At least mine do, and I've got a stack of the horrible things !!
But the Operator's Manual does say 400mm so.............. buggered if I know
Cheers
Nitram