Tranny problems, 07 model different than earlier models?

[lanceam24]

I have an 07 with missing second gear. Got everything torn apart and I see where it's busted. Now I have two bottom ends from earlier models like maybe 01 and 99. I was told they were interchangeable but they look completely different to me. Can I swap parts from the trans or should I just try and get a replace it? Also a few pieces of the sprocket shaft are chipped off

[Fix29]

99-04 400ex's didn't have reverse as the 05 and newer models do.

[lanceam24]

Yea but I read somewhere that they were interchangeable with the exception of reverse. I figured they just added reverse to the newer ones but I guess not. Upon further research I find that the gearing has changed and the countershaft splines are different and things like that. O well I guess I'll just look for a complete tranny. Or if I can find the broken gears.