I've posted a time or two on this forum about converting my Alaska work skiff from an outboard to inboard jet. The boat is a big, high displacement hull as opposed to a low profile ski type hull. I've got the conversion underway (here in CA doing the engine work, SBC 400 and pump rebuild, Berkeley), then to AK in April to do the install. My question is about the placement of the exhaust ports in the transom. Is there a "rule of thumb" for where vertically these are placed? I have center riser cast iron manifolds, heat exchanger cooled engine with a Comp Cams 268 cam so I don't think I'll have a reversion issue but I'm concerned about putting 8000lbs of salmon in the skiff and getting water backed up into the exhaust/engine. Is there such a thing as having the ports too low? If there is 12" or more of vertical distance between the bottom of the riser loop and the exhaust port which would be quite a ways under water, is that too much water pressure for the engine to overcome upon start up? Would this be the perfect application for some blocks between the manifolds and riser?