High Compression 390

Bypass the 'don't build it at all' for the moment; that is more of an economics position IMO than whether the 390 will work or not. Focus on what will work for this higher CR 390 design, and once you get where you are comfortable, THEN look at the cost and decide if you want to stroke it or not.

I did not realize that this had the NP trans in it, was used for load hauling, and you used 87. So that leads to the following observations:
- A 3:1 usable torque RPM range is highly desirable...actually necessary. I raced in a car with a <2:1 usable torque range and a 1.6 ratio step between 2nd and 3rd. That 2-3 gear step could be miserable when going uphill as you just weren't far enough up on the torque curve when trying to jump up into 3rd. So with your 2-3 gear step of 2:1. you had darned well better have a solid 3:1 torque band..... which absolutely means keep that CR up there. That speaks to your desire to have a smaller cam and higher SCR... both keep the lower end of the torque range alive. OR... AJ's suggestion for a trans change.... but the NP with the granny gear makes it a proper TRUCK so you really can't take it out, right? LOL (Besides, if you are on the farm...err, ranch.... a granny gear does come in handy.)
- The load hauling tends to make detonation a bit more likely. But a lot of that has to do with heat and getting the heads hot. So a good cooling system is a must and also goes along with a higher CR engine, because the combustion temps are higher with higher CR.
- The 87 octane makes things harder with higher CR. So that's working against you. 160-165 psi cranking pressure at the lowest altitude would be my limit, and for sure go with AL heads for ease of making it work. Also make sure you try for an effective quench gap; the .050" head gasket makes that less effective.

I KNOW I'd go with 11:1 kit without hesitation for your 5000'-9000' and have in my arsenal:
to bring it together. BTDT on this type of build a coupla times in my life. The wide torque range is why.