You'll have to modify the crossmember to make it work. The early fox cars had a crossmember that was a little more narrow at the ends, where it bolts to the brackets under the car. So the later models will be too wide on the ends. You can cut down the ends of the crossmember to fit or you can cut and re-weld the brackets to fit the ends of the crossmember. Stifflers makes a really nice aftermarket tubular crossmember that is a little pricey, but definitely worth the money. I have one on my 79 pace car and love it.
Another issue is the factory "double hump" crossmember made for dual exhaust clearance. I'm not sure if the 4 cyl one is different, but the later v8 cars were redesigned to clear dual exhaust. My 79 cobra had the early style, which only had clearance for single exhaust. However, it did have an aftermarket dual exhaust setup. The exhaust shop just ran that side a little lower, which works but isn't ideal. The factory double hump crossmembers are easy to come by and usually run $20-30. I have a, couple extras, but no idea where they went lol
