This is just a suggestion, and a suggestion only. I have been moderating Mustang sites for several years now, and the carburetor and intake system that works best for most Mustang owners with that engine is the Edelbrock system. Research the Edelbrock Performer intake manifold and the Edelbrock Performer 500 CFM 1403 (non EGR) carburetor. 650 CFM's is too much carburetor for your engine even after the addition of the roller cam, the intake and the carb. The heads on that Clevo of yours will accept either the 2V or the 4V intake and carb. That 73 Clevo is a dog when it comes to performance as it is set up. You have to remember (or understand) that we had to sit in line for hours to get a limited amount of gas back then, so these old engines were designed to not have a whole lot of power in order to save gas. The block and the heads are the same as they were in '69 when they were the muscle car of the industry, but things changed the cams, carbs etc. Blame this on the left wing government at the time.