I did something similar.. I had an original Mac Pro, which didn't support 64-bit MacOS because Apple's UEFI ran in 32-bit mode and Apple's boot loader / kernel

I did something similar.. I had an original Mac Pro, which didn't support 64-bit MacOS because Apple's UEFI ran in 32-bit mode and Apple's boot loader / kernel never supported switching into 64-bit mode from 32-bit mode. So to use that machine for 64-bit driver development, I had to make it into a "hackintosh", where they had a UEFI that would run in 64-bit mode..