Max HP limit for 360 magnum stock bottom end?

8psi? I don't see many issues. Especially with E85, it cools things down nicely. Your top end combo sounds better than most. A lot of guys take stock everything and boost it higher and higher, adding more and more heat to make power. You have alcohol, intercooler, and good heads that increase efficiency to keep temps lower but probably yields the same power.

I've heard first hand from Ram/Dakota guys running no more than 10psi and putting over 20,000 miles on it. Some even higher, on their heavy truck. Keep it from overheating and you'll be just fine. IMO