That ZIF socket was originally used in RS/6000 systems (same as the slots for the older PPC cards), so if you find some weird ZIF sockets or bizarre 604 cards that look like they should go in a Mac but are just cryptic and weird, they're probably for an RS/6000. I'm not sure if any of the RS/6000 series used any of the backside cache-style ZIF sockets (like the ones Macs have) and a cursory Googling didn't turn up much.
Anyway the particular example linked here is the fastest of the 750L series (one of the slightly faster, cooler-running copper variants) at 450MHz. It has the quicker BGA-style SRAMs which weren't very common on the early G3s or G4s outside of the PB G3 WS which occasionally also had BGA SRAMs on the very fastest ones (and the early cacheless 233MHz models usually used the BGA SRAM processor cards but without the SRAMs). It's easy to tell this is an IBM chip at 450MHz because it says so on the label
. Also IBM generally didn't laser etch the CPU like Motorola does, which is a dead giveaway as to who built it, but this also makes it more difficult to identify the CPU absent any other labels because IBM prefers to label the ceramic substrate instead, and this label is hidden under the CPU protector cushion thing. It's generally not advised to remove the CPU protector cushion thing because it's there to protect the exposed die from improper heatsink mounting or uneven stresses which will crack and destroy the edges of the die.
