@windg thanks! What timing is that? This is hot off the presses.
For what's it's worth, when following the instructions from @mitu it appears that you need to reboot (or maybe just restart emulationstation) for the updated script to take effect.
I rebooted and tried the "source" build again. Now I am currently in the middle of that source build, but at the very beginning it appears to be installing 6.7 but I won't know for sure until it completes (as some point while I am sleeping tonight).
If that fails, then it looks like I can now update retropie to get it with ease.