Who programs Mercury computers? Looking for more power from a 1995, 496 mag I do not know if it is true but i have heard that the 496 mag and the 500 hp are the same engine configuration excluding the computer.
Nope...496 is the 8.1 Vortec Chevy (LS style) based motor. Completely different than the spread port BBC style.
One option for you, being that you're a more hands-on kinda guy, may be the Dynojet CMD Marine unit we hope to release very soon. Plug-and-play piggyback fuel controller. Wideband A/F data integration and AutoTune capability. Check out http://www.dynojetcmd.com Tim, is this your boat/motor?