Good Luck... I do not think any of the companies utilizing LS based motors are going to offer manifolds that will work with Merc style spacers. Indmar also offers LS based motors but there manifolds are completely different. Plus most of the stock stuff coming out these days has to use cats which require a different exhaust manifold. CMI does offer some headers for the LS based marine motors. In fact Mast Motorsports offers a marine LS based motor with a set of CMI headers that APPEAR to have O2 bung located in the top of the collector.