440 what am I missing here?

Swapping a converter is a bunch of work. I wouldn't do that until I had checked all of the easy stuff. Compression check, firing order, double check timing, what do the plugs look like? How does it run at idle? What doe the vacuum gauge say? Good oil pressure? Have you replaced the FiTech with a known good carb to see how it runs? There are at least 100 things you should check on before you try a different converter.