I agree that water is very beneficial in your case. As I said before, it is very dependent on the application. If you are only looking for cooling, then water will work. You will hit a point where water will begin to retard the burn, and without timing advances, you could loose power, but that will depend on how you inject it and how much you ultimately use. You may know much of this already, it's just there is never really a universal answer to what fluid is best, which most folks are looking for. In your case, large displacement, no power addition wanted, no tuning changes, etc, a 50/50 mix will probably work great.

All of the parts in the 3 are perfectly fine with 100% meth, the pumps are what may be affected in the long term.