If you want to do turbo, and can find a way to make those work, go for it. There are plenty of OEM applications with log manifolds that look worse than those marine manifolds and they do well. Hell, some guys are even rear mounting turbos by the trunk and getting good results.
Looks like the plenum area is kinda big,
As opposed to, say turbo headers that have long primary tubes and snake all over the place before they see the turbo. Way more volume to fill on those before the exhaust gasses see the turbo.
