Snow performance sells what they call boost juice(50/50), and Summit racing sells it for around $7 a gallon. As long as you buy windshield washer fluid that is rated to -20, you will get the 30/70 mix. Snow claims more potential with there mix, but says you can run the 30/70 mix with good results. As for one kit, thats just a guess. I'll bet the pump is big enough to supply both motors, but you would be using only 1 controller, and the 2nd motor will be getting its meth from the boost reference of the 1st motor(2 kits would probabally be best).
I did ask if there is a potential to damage a engine. I was told that if you over inject, you will just kill the combustion and cause a miss. The system/pump injects at over 150psi, which gives good atomization, so hydraulicing the motor shouldnt be a concern.
I plan on running it on my 89 Mustang(351,fuel injected,Vortech,12psi+), and all the Ford magazines give the Snow kits good reviews. Snow claims they have a lot of fleet diesel customers as well. The Snow tech I talked to was very knowledgable. I would give them a call and pick there brains on a marine application.
LE