OK Fixed it. I tried a number of older bits of hardware here. One with a Core 2 Duo 6300 will run Debian12 Live (6.1 Kernel) but also stalls with the Rocky Installer.
I swapped the CPU in the machine that had a Pentium D to a Pentium Dual Core E2180 (SLA8Y) CPU. Approx a year newer. That boots the Rocky Installer just fine on the hardware that failed before with the Pentium D (SL9AP)
The working CPU (E2180) lacks Virtualization but has SSSE3 instruction set extensions that the Pentium D does not have. In that experiment Virt does not matter.
Thanks Ken