7C81 edit bitfiles?

My lathe spindle is powered by a large stepper motor which has its own stepper driver and power supply.  Currently it is run by a micro controller which handles acceleration, deceleration and running at widely selections of speeds, it also has an emergency stop.  The stepper motor has a 1:4 relationship with the spindle, one revolution of the stepper results in four revolutions of the lathe spindle.

There are just 2 wires connecting the micro controller to the stepper driver which amount to step and direction (the latter has been used only once to rectify direction), the lathe positively doesn't need to go in reverse thanks to screw on chucks etc.

The lathe is run by a G540 and (since I'm cheap) the mill shares the same G540 with a swapped X and Z axis.  The Mesa card does a great job with a G540x2D to provide the 5 stepgens needed for a 4 axis milling machine plus charge pump. 

So I'm wondering what I would need to do to convert the lathe motor over to being run by linuxcnc, for simplicity of wiring I would like it to go through the G540 on some of the unused pins?  I guess another stepgen would be needed?

The only documentation I can find on this is: 

wiki.linuxcnc.org/cgi-bin/wiki.pl?Editing_MESA_Bitfiles

is that up to date?
 
The G540 has spare pins on a terminal block on the back numbered 1-12.  1 to 4 are listed as DB25 input pins 10-13, 5 and 6 are listed as outputs DB25 pins 17 & 1.  I think that all of these become i/o if connected to an FPGA rather than a parallel port? 
 

The G540 inputs and outputs are fixed direction (and probably fairly slow)
I would use a cheap parallel port type BOB on the second 7C81 connector
for the spindle (plus it would add some more I/O)

Wow! I shouldn't make assumptions like "Geckodrive will have made the connections straight through" without checking the same!  Thanks for putting me right.

Makes me even happier that I got the 7c81, would a C10 board work for P2?

Have a great weekend

Yes, a C10 should work fine with a G540 (or any parallel port type) pinout