C64 Cost-reduction Prototype? ASSY 250458/PCB 252101 REV.1

Folks,

I've had this C64 for a few years, and it would need some attention to be
functional, but it was immediately obvious to me that it wasn't a normal
machine because it has a flat-flex keyboard cable. Then, when I looked
closer, most of the chips are normal, but:

1) The ROM is an EPROM, and appears to be a combo basic/kernal
2) The IC in U6 is purple ceramic, and clearly has a hand-stamped label,
"240431", which doesn't match anything that I am aware of. Based on
location, it's a 6510 of some variety, but maybe a test production run of
the 8500?
3) There are extra wires on the keyboard itself (which is a Mitsumi
membrane)
4) The board has a SuperPLA, 251715-1
5) The RAM is 2 64k x 4 HM50464-15 chips like the 250266 and 250469

I'm sure that there are other oddities. I've shared a quick album of photos
here:
https://www.icloud.com/sharedalbum/#B1f5BydzFLHLGD

I've not attempted to power up the machine and would need to at least dump
the ROM first.

Any thoughts/comments are welcome.

- Alex