Brake Master Cylinder

When I picked up the car it had a firm brake pedal.  I got it home and rolled it off the trailer, it had a firm brake pedal.  I decided to flush out the old, nasty fluid with fresh and half way through the something happened:  The pedal went to the floor, air blew out of the brake bleeder and the master cylinder started making a grinding noise.  No matter how much we tried, we couldn't get the air out. 

I removed the master cylinder and when I took it apart I found lots of rust and pitting in the bore.  This is not the original master cylinder for the car.  Somewhere in 2127's life, a master cylinder off another car was fitted using this aluminum adapter block.  In the picture below, you can see the aluminum block between the master and the brake booster.

This is all great except for one problem;  I have no idea which vehicle this master cylinder came off of.  After messing with this for a couple of days and even buying a master cylinder that eventually did not work, I stepped away from this and did the steering.  After that was done though, I had to figure this out.  The only clue is a casting number on the bottom of the master, "29929".

I tried googling it with no success.  Then I found that the Cardone website has a guide that includes casting numbers.  I finally was able to figure out that this casting was used for 75-80 Chevy trucks and 78-86 Jeeps.  I found a Jeep master cylinder at the local parts store but the plunger was different.  I then found one at another store for the Chevy truck.  It looked identical in all respects so I got it and installed it.  Not quite sure what the braking performance will be like but I do at least have a very firm pedal now, which is fine fore the moment.  I'm not planning on any aggressive driving but rather just to get the car on the road and see what I have.  At some point, I plan to revamp the entire brake system including a master cylinder more appropriate for this car than one off a truck.