See My XR-SM
A friend bought some XR250 hubs to try & go the cheap route to SMing their bike. The rear hub's the same for the XR250 & the XR400, so we tried my SM rear in the XR250 swing-arm before getting the work done. But the front wheel spindle is a differant size between the two bikes so there wasn't any point in trying my SM front wheel in the XR250 forks.
From what I can remember the Honda CRM250 Mk1 wheels also fit the XR400...but i'm not 100% sure