Or just go with the modern replacement, Holley Street Demon. It's basically a TQ with all the needless emissions crap taken out and modified to fit on a square-bore flange. It's advertised for gas mileage and response on the street, best of all you can buy one NEW instead of taking a gamble on a 40-year-old lump that still may run bad after a rebuild and tune. I like ThermoQuads but gave up on them it's just too hard to find good cores and parts anymore, not to mention spread-bore intake manifolds.
That carb (and appropriate intake) on a stock 5.2L Magnum would probably get the best mileage you possibly could out of an SBM, except for maybe a built 273 with similar compression, heads, and roller cam.
