I was unsuccessful in getting the PGX64 to work using the mach64 driver,
fortunately however there is the fbdev framebuffer driver which works fine.
So now I have a LXDE desktop on my Ultra5.
https://feilipu.me/2018/04/14/old-sunshine-migrating-ultra5-to-sparc64/
I was advised that trying to pursue the ATI Rage mach64 path is not worthwhile.
There are lots of support issues lurking around the corner in a year or two.
So as a next step, I'm going to try to get a Sparkle GeForce 9500 GT 512MB PCI video card working.
Really happy that my old Ultra5 machine still has some relevance.
Phillip