https://lmr.com/item/M9000PMCM/ford-...X8QaAoRm8P8HAQ
The expensive route... But the hp is there.
Honestly with 140k miles I'd do header back exhaust, rear end gear and axel setup to 31 spline, trans wise you have the right idea and not boost the motor. It would last alot longer. 450+ hp on stock bottom end is a matter of time til something let's go.
I settled long ago for all motor on the mach so I'm biased , but if I wanted boosted mustang I'd buy a cobra or Shelby.