I have talked to a mechanic who is currently working on a kikstart. He is not using a XR400 sidecase. I seen the bike. As for how it is going to work you would have to ask him. His site is: http://www.geocities.com/gtthunder.geo/
GO there and then email him or call him.

Griff's FSR

 

Here's something to consider. Forget about the side case cover for a moment. What about the inside case half. Is it going to accept a kick start assembly(the small shaft and gear that engage the clutch basket gear)? Is the case half machined for this or is there the physical room neccessary. I don't own a 400EX or have ever tore one down to know for sure. Hope this helps.

 

400EXalltheway You could just save all your money and push start it. That way you could take ALL the weight off including the weight of the kickstarter, battery, starter and once it gets going just don't stall it (like indy cars do). That way you won't even need new cases. Push starting is easy if you have a friend to help you out or better yet get pulled by someone on a utility ride.