The guidance from Yanmar is that if the exhaust inlet to the ell is 8" or less above the water line, then the upside-down U outlet is necessary along with an anti-siphon valve on the cooling water line to the ell.. This was noted in the 2QM manual, but I am thinking it is the same for the GM.. If you have a U shape, then ya probably should go back with same.. If a straight one, then you may be OK with the stainless part?
Of note on that stainless outlet is that the Yanmar cast part (not the U shape) has the exhaust in an inner tube.. the water flows in an annulus prior to being dumped into the exhaust stream through a circumferential opening a couple of inches downstream of the hose connection.. May not make a difference other than the OD of the tube running much hotter, but ya never know.
EDIT NOTE: The water inlet to the hot gas part of the outlet pipe MUST be lower in elevation than the lowest part of the exhaust outlet port of the engine, otherwise water will get into the engine. The annular opening inside the Yanmar part (where the water comes out into the exhaust stream) is an inch or so below the gas inlet to the elbow. It looks like there may be an annulus in the stainless part, but I can't see the place where the water gets mixed into the exhaust stream.
