The 120 front is no problem.
I'm thinking of putting a fatter set of tires on my 250. I'm thinking of putting a 160/60 on the rear but will that fit without any modifications?
There are a few 160/60/17 tires that can be installed on a stock rim, however most tires in this size are not designed nor recommended for a rim smaller than a 4.5 inch wide rim by the manufacturer. With certain 160/60 tires there will be minimal clearance and removal of the chain guard may be necessary. It is highly recommended that you mount a 160/60 tire on a 4.5" rim (which are available.)
A Michelin Pilot power in a 150/60/17 has been done before on stock rims with no issues.I'm looking into Michelin pilot road 3s. Any recommendations? 160 or 150