The reverse was also true; I worked for a company back in the 1990's that provided third part SPARC solutions - probably the only company in the Southern Hemisphere at the time that did so.

One of the more interesting products we resold were the ROSS Technology "Sparcplugs" - you basically had a SPARC motherboard and CPU that fit into a couple of 5.25" drive bays on a host PC. So almost the reverse of the SunPCI cards.

https://computers.popcorn.cx/ross/sparcplug/

Back in the day, those types of cards were available, though a little uncommon:

https://en.wikipedia.org/wiki/Z-80_SoftCard

https://en.wikipedia.org/wiki/Apple_IIe_Card

https://www.applerepairmanuals.com/the_manuals_are_in_here/P...