Crossett

This page says they have forged rods, just not pistons.

http://www.perfprotech.com/store/art...fications.aspx

Regardless, excessive cylinder pressure or RPM are what will kill it. I would think you should be able to get away with a fairly aggressive heads/cam/intake/carb combo that should make at least 500 hp and be good as long as you don't spin it too high.

Sport 280

If you have a 365HP engine that is rebuildable, and you plan to supercharge it, contact rmbuilder (on this site) at Marine Kinetics. He is one of the best when it comes to cam setups. You need to know if the 365 heads are in good condition as well as the block and rotating assembly, one common problem with the old Mark IV heads was cracks around the valve guides.

Another route to building 525SC engine ( about 500 prop shaft horse power) would be to re-cam the 365 with a crane (old number 132561 hydraulic non roller cam that came in the old 400, 405, 420, and 525SC Merc HP series engines.) you need the above cam, valve springs, crane gold roller rockers, gil manifolds, and a Weiland 177 blower and holley 800 DP. There are likely better cams available than the 132561, but this is the cam Merc used for the above engines.

You could also contact Comp Cams and tell them what you are building and they likely can suggest a good cam for your build.

As always, horse power just depends on how thick your wallet is.