I think there may be a few examples, but not best suited to the airframe due to weight. A more popular consideration is having a rebuild done where the angle valve case is machined for parallel valve cylinders. The larger engine shops (like Barrett) may have more info on this
Has anyone installed an IO 540 angle valve on their RV10?
I agree the parallel valve is the preferred option. I have had a rebuilt angle valve offered to me for practically free. So I'm very interested in what it would take to mount. Cowl mods do not worry me much. Mounting the engine is my main concern.