Greg Hillyer walks through the welding and prep work behind one of the more ambitious Mustang modifications an owner can attempt: converting a 1966 coupe into a fastback by grafting on a donor roof. It’s a job that demands precision most home builders never attempt, and the stakes for getting the fit and structural integrity right are high. At least one viewer credits a direct conversation with Hillyer for the success of their own conversion. Watch to see exactly how the roofline transformation comes together.