Non-standard parallel port on Selectric I/O?

I have what was once an IBM 2970 Reservation Terminal. Some time in the late 1970s. an outfit called 'Western I/O' got hold of a bunch of these, including mine, ripped out all the IBM electronic guts (but left their electromechanical bits - solenoids and contacts) and installed their own boards, and sold them to the home-brew computer folks of that day - presumably hung off contemporary Altair and Imsai machines etc. They made two versions. One was a fancy full-blown terminal with a 6800 microprocessor, adjustable baud rates, standard RS232 port etc. I'd really like to get hold of one of these if anyone has one gathering dust btw... The other one was a very dumb print-only versions. According to contemporary ads, it has: "? Printer-only model availability w/parallel ASCII interface." "The Printer Terminal IBM Selectrics are known for their well-defined, high-quality printed characters and easy-to- change elements. An ideal choice for text processing, highly-legible source listings and personal or business correspondence. And it's easy to connect to home or business computer. Just plug in 115 Vac, hook up the ASCII printer port and let 'ergo." That is ALL the documentation I have on this thing! The 'parallel ASCII interface' is implemented as a DB25 female on the rear of the Selectric. It *looks* exactly like a parallel port on a PC. So I hoped it would use standard parallel port pinouts and a straight-through ribbon cable would do it. No such luck. I don't have a parallel port analyzer, but I have lots of serial port analyzers, including ones with an LED per line, all 25 lines. So that is an improvised window into what's happening. For starters. when I operate the 'paper out' switch, I can see a line going high/low corresponding to switch position - but it's pin 19 on the DB25 connector, which should be ground on a standard parallel port! 'Paper out' should be on pin 12. So it's clearly not standard... Now I can start tracing pins on the interface back to lines on the PCBs, and try to figure what they do. At least I can relatively quickly eliminate those that aren't used, or are ground plane. But, question: back in the day, was there *another* 'standard' for parallel port pinouts? Used on S100 bus PIO etc. cards, the kind of thing this product was intended to be used with? I've found Googling on such data to be remarkably unproductive... any help out there? Mike