Will,
If I were looking at doing this swap, I would drop the additional cash needed to buy a set of the CHI 4V heads. The 4V head is a 3V head that has had the intake port opening tapered to the dimensions of the 4V port, so that it mates up directly with any 4V manifold. Other than the tapered opening, the intake port is identical to the 218cc 3V intake port. This would alleviate the need to modify the intake manifold for the IR system.
You are not going to notice a difference in performance between the two cylinder heads. Set the 3V heads on the shelf in case you decide the headache of owning an IR system is not for you. By keeping the manifold unmodified, it will be easier to sell if that day should ever come.
My advice for what its worth.
take care, cowboy from hell
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