Shift fork problems...

[Spitfire]

Hey,
I'm in the process of putting the bottom end of my 1997 RM 250 back together. I had the tranny apart, and am having troubles putting it back together. All of the gears, snap rings, washers, and other parts are on the main shaft and counter shaft correctly, I know that for a fact. When the main shaft is through the bearing (I'm installing it on the clutch side of the case), I go to put the shift fork on, and the guide pin on the shift fork does not go into the appropriate groove in the shift drum. The shaft will not go down further, but it's almost like it has to, the guide pin needs to go down about another 1/16" to fit into the shift drum groove. I'm not positive this is the right groove it should go into though (my Clymers doesn't tell you much about installing the shift forks), but it's the most logical, it's the bottom groove in the drum, if you're looking at it from the top (once again, the whole assembly is in the clutch side case). Anybody have any ideas about what's going on, any help is appreciated!