I've done everything you describe. Currently have Langdon's cast iron (Fenton style) headers, Sharp dual carb intake with the 2 barrel carbs Langdon sells (run great right out of the box) with the plate for pre-heat, his carb adapters & air cleaners. I plan to change back to dual stock carbs and have them rebuilt by George Asche, because I like the look of the original carbs. I'm also using the HEI Langdon's sells. If you decide to run a dual carb intake with the hot water pre-heat, make a gasket from gasket material/sealer for the plate. DO NOT use a stock gasket that is used where the stock intake/exhaust bolt together. It is a piece of aluminum (?) sandwiched between gasket material, which WILL leak coolant (did in my case TWICE til I figured it out). Good luck.