Looking for some info on upgrading my hp 500's, i'm looking to change the cams to crane 168741, and go with aluminum cylinder heads, does anyone have any suggestions on what heads to use and also what valve springs are the best to use. would it be best to go with an MSD ignition or keep the mercruiser ignition.

Thanks

You need to match your cam to your cylinder heads flow rates. The 741 cam is a mild upgrade for the stock heads.