I bought a pair of brand new DANA HP 900's off Ebay for $950 for our 208 Islander. It was Santa's Christmas gift to himself this year.
Anyway in searching magazine articles I found a write up on mounting Eddie Marine tabs (same tabs as my Dana's) and they didn't match the deadrise or bottom of the hull they mounted them horizontally level.

Any one ever see that? Any experiance with it?

Sort of like this?

Depends on what you want to do with the tabs. I mounted a set of Dana's on my hull close to the bottom and as close to the drive as I could. This allows me to put some hook in the hull when I need it on Lake Michigan. Being long tabs they have a much greater effect being in and down level with the bottom. They also can create drag if not postitioned properly. If you using the tabs to just get on plane then the normal mounting is good. The horizontal mounting in the picture above, I would think would create down force for the bow, where as parallel to the bottom surface will tip the hull from corner to corner. I am only guessing at the horizontal situation, I have never messed with it, so I have no experiece. Maybe Mr Velocity can comment on the effect of that mounting situation.
Hope this helps..

Dick