32 Bit UIDs For Unix?

Ghidra asks: "I work for an ISP and we now have UIDs greater than 65535. I thought by upgrading to Linux 2.4 (and having fairly current utilities) that I would be able to support these UIDs. Unfortunately, it doesn't look that easy. It also doesn't look like there is much help on the Internet on how to accomplish this. Things like ls, ps, chown, and the like just don't want to recognize these high numbered UIDs. So what kind of steps do I need to take to upgrade my system (Slackware-current) to support 32 bit UIDs?" What other Unix variants can benefit from this information, as I don't think Linux is the only Unix-clone that still uses 16-bit UIDs. Are there any flavors of Unix that have already solved this problem?