I also have an
8086 board for the XT. Of course the
 benefit of that
 processor over the 8088 was the 16 bit databus,
 which sould be lost if
 the thing had to do 8 bit accesses to memory. So
 there's  full 640K of
 RAM on this board too. Of course it does use 8 bit
 transfers to access
 ROMs and peripherals. This is a full-length card,
 again with a cable and
 DIL plug to go in the 8088 socket. 
  Is it's intended to supplant or supplement the 8088?
 Are you sure it just isn't a mpu board for some unit
 w/a passive backplane? I don't mean to insult your
 intelligence, just that it's a possibility. 
 
I think the name etched into the copper implied it was an add-on for the
PC/XT, and given the fact that it has this ribbon cable ending in the 40
pin DIL header plug, I assume it replaces the 8088 (and therefore doesn't
go in a passive backplane).
-tony