The Roush packages can consist of many different performance options. Most the dealerships that offer a Roush package usually are just bolt-on suspension parts, with interior upgrades. There are some that have engine upgrade, nothing internal just bolt-ons as well, i.e. supercharger, air intake induction or a gear change. The latest Mustang is actually modeled after the 65-66 fast back, the front ends look very similar as well as the rear-end, wheelbase is close as well. I love what Ford did with the Mustang, nostalgic look with new technology. Unfortunately it isn't as easy to make performance upgrades as the original muscle cars.
I currently own a 67 Ford Fairlane GT, I set it up for drag racing. Use to travel all over for bracket racing. Somewhat of a motor-head. I'm a Ford guy as well. Certainly would love to have that 69 428 CJ of yours. The 427 side-oiler was one of the best engines Ford built. The Thunder-Bolt came with those, Galaxy had an option and also the SC Cobra( the baddest car Shelby ever built). The baddest engine was a Ford the 427SOHC ( all hand built) nothing touched the horse-power and torque that those produced. It was band from NASCAR in its day because MOPAR & Chevrolet had nothing to compete. You want to see some awesome cars, go to Norwalk during the NHRA Summit Racing Nationals end of June. Start talking cars and I'm all over it.