IC 2 M27C1001 labelled AR8000-00135-008-104

This is an 128K x 8-bit EPROM.

The data appears very sparse, to say the least.

00000 to 01fff: all FF
02000 66 23 80 3f 66 3c 41 3f
02008 to 1ffff: all zero

which disassembles to this

0:  66 23 80 3f 66 3c 41    and    ax,WORD PTR [eax+0x413c663f]
7:  3f                      aas

 which does not look like useful code.

I think it is two little-endian 32-bit vectors:

3f802366
3f413c66

Underneath the board are two Intel E28F008S5 surface-mounted flash ROM chips. That is 2 Mbytes total enough to store the ROM-based DOS. I will have to read them when I have the board up and running.