Thanks. SIP is disabled. The kext unload/load did not allow the VMs to start normally.
I found another forum that mentioned that VBox 6.1.x on Ventura will not start VMs in normal mode, but that headless mode will start and then you can remote desktop into the VM. Headless start (only) does appear to work in Ventura after following your Sonoma guide -- the "preview" thumbnail in VBox shows the guest running normally. I have no clue why that is and VBox does not appear to be able to give useful logs for the failure when launching in normal mode. It does not appear to be a function of the guest VM settings, as I have tried to disable/toggle as much as possible on multiple guest OS types and headless start does not have any issues.
Again, your guide works perfectly for Sonoma on AMD and VBox guests run normally, so apparently this broke in Ventura and was fixed in Sonoma.