before you invest in a lot of carb replacements, you might try having a carb shop open up the main jet on your 5200. most were jetted really lean..and most of the rebuilds have unknown jets.. you really cant go by the "jet size" numbers.. if the car bogs or has a flat spot, find a good cam shop with a set of jet reamers and have them open up the jets .005 to .010 to start with.. when I got my 73 it had a "rebuilt" 5200 and had a serious flat spot, I had the main jet opened .010 and it runs like a champ.. also you might want to cut away about half of the throttle spring so you wont need to put two feet on the accelerator pedal.. also...
best thing you can do to a 4 cylinder pinto is to get an adjustable cam pulley and advance the cam about 4 degrees.. lowers the power curve and increases torque..
experiment with the advance to get best performance for your car but not more than 6 degrees advance.
look up racer walsh.. he has the parts..he also races a pinto on the SCCA circuit..
http://www.racerwalsh.zoovy.com/ tell brian that ed with the lil red wagon in texas sent you...