The 68k chip in this unit was produced the 33rd week in 1989 (Sun. 13 Aug, 1989 - Sat. 19 Aug, 1989). Given lead times, that puts the motherboard production time frame into later 1989 reducing the possibility of it being an early prototype of sorts.

Well for now I am going to work on getting it running once the capacitors arrive. I hope the old Conner drive has some life left it in!

Edit: I take that back, worked on inventory assumptions. For fun I looked at my two Original Macs. One is pure original, yet the CPU is newer that the unit with the swapped in 512k motherboard. Weird.