different rims front and rear will be fine provided he uses the same size tyre front and rear, and very similar offsets. Changing a rims width does not change a given tyres diameter. A radial tyres diameter is controlled by the steel belts in its construction and has nothing to do with what rim its stretched over.

but i think trying to fit 10inch rims on any subaru without some very serious suspension, and body mods is gonna be troublesome.

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Doing it for all the wagons out there