That came from the obsession with Hemi heads which do offer large vales relative to other options and the lowest volume:surface area. Unfortunately they also are inherently low compression unless the piston has a high dome. Fine for low compression low rpm motors, but a high dome makes flame propagation a slow and inefficient process. That's why on my CB77 race motors, I machine "a lot" off the heads and use lower dome pistons to get the smallest possible total surface area at the same time as highest compression (we're still talking small numbers).
I use modified CB350 pistons for years because I could machine them to get a decent squish band, lower the barrels and then machine a matching squish band into the head. Those pistons have thick heavy rings which are an impediment to high revs but on a lower revving motor, they work fine. Unfortunately that is the path with the most amount of work and cost, but hey, can't have cheap, fast and quality can we?
Those motors need a serious amount of spark advance with high domes and that speaks volumes about the inefficiency of that design. Go with lower domes, machine the head and pistons if necessary to get an angled squish band and reasonable compression and run much less advance.
They have a 360 degree crank, so a siamese inlet is not a problem, but the inlet tracst do need to be opened up a little and try a CB750 carb. Same slide diameter as a CB77 carb but taller oval shape, so the same at low throttle openings and bigger at WOT.