I have seen some Fendt 300 series with front axle spacers for 120" spacing.  The same tractor had some rear axle reinforcement however.  I have seen some New Holland T7 and Deere 7430 adjusted to 120"; however you better forget heavy loads on the rear axle, and same goes for the front axle (when they need to put heavy front loads, they usually install stretched front axles).  I'd say a Deere 7810-20-30 would do the job, front and rear.  Or an older Genesis.   But I would be afraid to go to small frame models.  Shoot me an email if you want.

Nick