[Jillbert11]

have a 96 fourtrax 300 and the engine is done. have a lead for an engine out of a late 90's 400. will the 400 fit in place of the 300

 

[Jeepwm69]

No. Not even close. Would require an incredible amount of custom/ fab work.

 

[mac102004]

It would be a heck of an accomplishment if you were able to pull it off.

 

[SamUK]

A 350d engine would be a closer fit I should imagine and those require a generous amount of fab work too.