Cliff,
It sounds like you have a typical race master cyl. setup. Dual cylinders with a balance bar.
First try disconnecting the pushrod from the front cylinder and try to arrange the pushrod to get a full stroke on the rear M/C..
Also, you should bench-bleed it if the fluid all drained out. This means disconnecting the outlet from the M/C, running a hose from the outlet into the reservoir, and pumping the piston several times to pre-fill the cylinder.
Another method is to use a vacuum-bleeder. I've had good success with them.
As far as the cylinder itself, it could be a Girling, Wilwood, or Tilton. The bolt spacing is standard for these units, but be sure you get the same piston diameter you had before, or you could upset the brake balance.
Check
http://www.summitracing.com/ or
http://www.jegs.com/
They both carry Wilwood and others.
Good luck,