OK...here is a new twist on the debate. While doing some research on do it yourself carb to efi conversions I came across "Mega Squirt".
It's an open source, build it yourself, PC programmable ECM that I'm considering using to convert a simple GM TBI system to my boat. So far everything seems to be relatively simple and understandable.
What I'm struggling with is how one would set up the fuel delivery from tank to high pressure pump. From what I can tell, most factory systems use a two pump system, one low pressure to move volume from the tank to the engine, then a high pressure pump to supply the right pressure to the injectors. Would it be reasonable to use the existing mechanical pump as the low pressure pump and just install a high pressure between the low pressure and the injectors?
Another alternative seems to be a fuel control cell like PCM uses. But again with this setup, is it reasonable to use the mechanical pump as the low pressure feed pump or would you have to replace it with an electrical low pressure pump?