Get the intake lobe of the cam you are looking at on both lobes, the extra exhaust duration is contaminating the incoming charge as well as opening while there is still some cylinder pressure burn down pushing on the crank.

As for the intake manifold I agree with the stock spreadbore intake, they are a lot better than generic motors or ferds intakes were in both performance and fuel distribution and depending on the size of the tractor you are pulling the extra weight can be a good thing on the front of the truck. Just spend an hour or so smoothing/rounding the carb to port transition and smooth out any bumps/protrusions/casting flaws, block the crossover with epoxy and be done with it.