So I just went down to 8 in the back...and apparently had nowhere near the clearance that I thought I did, even with the c-notch. It bangs way hard. May I recommend an underbed notch to anyone who wants to go down that far? Lol.
Gonna give it a few weeks to decide if I'll keep it there or come back up just a little. First impression is that I can deal with it.
The pinion angle still needs to be adjusted, but otherwise the driveshaft should be fine. I only had a 3/4" gap before contacting the output seal after going down 6 1/2, but any change here was pretty minor.