I didn't know what kind of setup you had on that 400 until I checked a parts listing to see. Then I realized that you can't just slide the tubes up through the trees. Actually, I kinda figured that if it was that easy, you'd have already done it.
Only thing I can offer is too consider swapping out the front ends. I definitely wouldn't attempt cutting fork springs to drop it cause you start messing with spring rates then. Somebody here might be able to offer suggestions on forks that might fit w/o much modification. I'll also do some research, if you want to go that way. Just let us know what you think about that.
For those who don't know what
THAT 400 front end looks like, here's the upper part of the tree.
Later on, Bill