Thanks to all for answers on my original post. I have a 1987 vintage 350 Magnum thru transom exhaust, and my original plan was to do a complete rebuild and up to around 400hp. I'd like to do a quick fix for the season, then do it the right way later. What are the "standard" hp upgrades I should do for this engine? I was thinking (easy) upper end stuff for now, induction, ignition, maybe cam, and do the heads later. Any thoughts? What is a good cam choice, carb, intake etc.

Best place to start is wioth Dennis Moore's book "Small Block Chevy Marine Performance".
In the book you'll find everything you need to build what you want.