They used to sell weld on adaptors to add more carbs to your stock manifolds.. I reworked the heads on my corvair dunebuggy. heads and manifold were a one piece casting I was teaching a cyl head auto shop class at the college. they had a head machine. I bored extra holes in the aluminum heads. surfaced the top flat made the adaptors with a step, a four bolt top flange then used epoxy for a sealant. drilled and tapped the head then used two holes for bolts to pull the adaptor into place and two for the spider manifold to bolt on to. with a 500 holly 2 barrel It would do wheelies in second gear.

I also took a stock V 8 two barrel manifold and hogged it out on the milling machine to have two long slot openings then machined a 4 barrel adaptor plate to fit on top. I ended up giving it away. installed a 460 ford engine instead of finishing the old motor. I've moved and haven's seen how it worked for the guy.