They will bolt on with necessary brackets etc. Upgrade of calipers of 2.0 turbo legacy are better option on the legacy due to them having 316mm discs compared to the 294 on the 4pots. What size wheels you using with them?
17 wrx alloys,should the 4pots not just fit straight on....dont need bigger brakes as its bog standard 2.0l,just going to be used for towing etc etc....