Hate to throw cold water on the fire, but my gut tells me that this is just a generic PC clone case missing the skins. The removable motherboard tray is a very common feature of "middling to good quality" PC cases, and the skins probably consisted of four parts: a snap-on plastic bezel, two "drop-down" or "tip-up" side panels, and a slides-on-from-the-back top that holds the side skins in place when it's secured. (Or, alternatively, it may just have consisted of the front bezel and a one-piece "U" shaped cover.) In fact, this case looks a *lot* like several cases I owned in the 1999-2004-ish time period. (Perhaps even a dead ringer for a particular 400Mhz Dual Celeron box dating from the beginning of the period.)

If the only evidence you have for some sort of "prototype" connection is that little Apple logo stamped in the metal, well... okay, here you go:

The tray the CD ROM drive is sitting on is from a PowerMac.

HOWEVER, look at the design of the case: peripherals in the 5 1/4 drive bays are *supposed* to be fitted with little plastic or metal mounting rails, allowing the device to be slotted in from the front and secured with screws. I think someone used that mounting tray because they lost the rails; note how the drive is sitting in the *middle* of two of the drive bays because the mounting plate is screwed into holes that are meant for the rails which would be at the midpoint of the drive when properly mounted.

In other words, well... it's junk, not a prototype. Sorry. :/