That would be cool but yeah clearance will be an issue.

Sorry the approach angle of oval port heads is a bit different, for round port heads what you have is fine, although there is one last very sharp turn from port runner to valve inside of the A12 round port heads. Don't forget the oil filler hole in the cover. It might be worthwhile putting a join mid way along the 'U' of those runners so you can disassemble relatively quickly to fill oil or check tappers/rocker gear.

With an oval port head, if the approach angle of the runners can suit the angle of the ports and lead down into the cylinder you (I would think) gain better flow.