umm what would be the reason? I seriously think that now matter what, you are going to get better results with the OHC design. If this were a better way then people would already be doing it.
only advantage (and its minimal) is moving useable torque to a lower RPM range.
OHC is the way to go, it is way more efficient and gives you the quickest cam to valve interaction. The cam is closer to the valve and there isn't a long pushrod to be pushing up and down. That is why almost all manufacturer's have gone to it on most vehicles.
You would need a custom made block, head, cam to do this, might as well buy an Iron Duke it is a 2.5L. There is no place for a cam in the engine and there is no way that the head could be modified to support this. Even with a alternate head you would have no place for a cam. for all the money you put into it the Iron Duke would be a better/cheaper choice.
BTW the Iron Duke is a 2.5L 4-cyl built by GM.
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