E Tops have a 15 1/2 inch primary into a 4 1/2 inch elbow.

They look good but do they help or hurt power?

That would depend on what you are comparing them to

I would think these would hold up well against e tops, and pretty much any manifold except the old Kieth Eichert's. Against a Sport Tube or some other long runner header I think they would start restricting power???

Are those 02 sensor plate something you had machined or is that available from a vendor? How do they affect the fitment at the transom?

I don't think they will restrict power , But in a naturally aspirated application they won't be able to scavenge exhaust and gain you some extra power like a long tube header will.

we made them up at Island racing. Put a small wedge in when running them in the boat to compensate for added height.

don't have a honest answer to that as we didn't run any comparisons. I'm sure we left some on the table with them but we were happy with the results.