If you have that intake manifold type, then you have hope. It can be made to work reasonably well. Just forget about using the vacuum signal, the fine tuning of that requires a lot of work, and possibly mods to the carb and some select secret tricks of the trade I'm not about to reveal ;)
You would get better throttle response from the Kadron kit, and better mileage assuming you don't have an insanely heavy foot.
You are looking for an economical solution.. that to me sounds like "use what you have and see what you can get out of them first".
I used centermounted 40mm duals for years in smaller dispolacement engines (1700 and down) and I just accepted the less than perfect low end. Had them tuned by race pros on several occasions, never got them to work "just right" at low rpms. But very close :) Takes patience and tweaking of the carbs and distributor. I had/have a dual advance distributor with adjustable vacuum mechanism and well the centrifugal advance system always was adjustable from the get go. (if you knew what to do). Trial and error, like there was no tomorrow. Hehe
I'd like to get my hands on your engine... lol.. this is interesting..
Jan