Update! 1/26/17:
Thanks to finding documentation for an Intel Above Board 286 we had lying around, we found that the board can be configured to work in an XT-class PC with 8 bit bus. After multiple rounds of swapping 256K RAM chips we finally found a set that works and configured the board. Happy to say that we now have the full 640K on the XT.
Excellent condition IBM PC/XT model 5160, includes 5.25″ 360K floppy and Seagate ST-251-1 MFM hard drive and currently has 256K of RAM. The RAM expansion board in this system was unfortunately damaged by a leaking real time clock battery, a common problem for machines of this age. We hope to repair or replace that board soon to have the full 640K. This machine also has a mint condition Model F keyboard, and it pairs perfectly with our recently restored IBM 5153 color CGA monitor.
Serial number: 62857525160
System complete with matching monitor:
System cleanup and testing:
Bad battery:
Outstanding model F keyboard: