A 300+ HP 302 these days is easy, especially if you are going with EFI. I can name you dozens of cars I have known that have hit the 300 RWHP number in Fox Mustangs.
My buddy had a 94 Cobra that we did nothing but bolt ons to. It had Gt-40X heads, a Crane 2031 cam (Crane's E303), long tube...