I have stock 454efi mags. One mechanical fuelpump went bad which led to a 4 hour 25 mile limp back to the ramp. I replaced the pump. Question, Can I install a crossover line from one engines mechanical pump discharge line to the other engines mechanical pump discharge line so if one pump goes bad both engines will continue to run off of the one good pump?

I would say it could be done if you were to still idle or a slow cruise. I wouldn't want to run it very hard do to possible leaning out and having some detonation going on. But than again I seen Macgyver do some impossible stuff!

Do you have the water pump/fuel pump belt driven assembly? If so, the crossover number for the Merc fuel pump is an Airtex 60932 which can be purchased for $70 at an auto parts house. Throw one on the boat.