[U47]

If I was really going for mileage I would use part # 518111 (A). If you are going to do some towing your going to have to compromise just a bit so I would use the #537441(E) or the 9777254 (U). I would use the stock iron Q jet intake or a performer with a Q-jet . I would use iron RA111 exhaust manifolds so I wouldn't have to richen up the carburetor jets like you will have to do if you used headers. I would recurve a HEI-mechanical all in at 2,000 and make the distributor advance run off manifold vacuum. Try to get a adjustable vacuum advance and give it as much as it will take before detonation. No EGR, but use the thermostatically controlled air cleaner, the kind that has a snorkel to the inside of the fender for cold air--the other earlier type when fully open will just get hot air from the radiator so use the newer type (1970+). If this is a automatic I would use the tightest converter I could find ( most likely that would be stock ). With a non overdrive and a 2.56 rear end you should expect 22-24 mpg in a 4500lb+ clam shell Catalina wagon @ 55-60mph.

D.