OK, good news, Ghostscript has a IBM 3852 output driver. It appears to use ESC codes that correspond with the PJ-1080A ESC sequences. Try hooking up the PJ-1080A to a machine running Ghostscript and see if it outputs correctly with the 3852 driver.
I had some more time to fiddle with this. My Canon will not print properly with the IBM Ghostscript driver... it spits out pages of Japanese characters.
Andy, your ROM link is dead. Could you share it another way?