Do I have the right master cylinder ??

[Bernie]

I've been having trouble bleeding my brakes and centering the combination valve and got to wondering if I made a big mistake at the start. I have a K20 with the axles off a 1978 k20 so I have discs at the front and a 14 bolt rear with big drums. I bought a combination valve and new master cylinder. I mounted the valve up beside the MC, the frame was bare when I got it so I don't know much about where the brake lines should go. I thought that the bigger chamber of the master cylinder works the disc brakes, the bigger chamber on mine is at the back near the booster and I connected the brake line from the back of the MC , under the bigger chamber, to the port on the valve nearest the take off port for the front brakes. I looked at another master cylinder and saw that the bigger chamber is on the front. Were there two sorts of master cylinders made with the chambers swapped over ? Was I right in thinking that the front intake to the combination valve is next to the exit port for the front brakes ? I know which is the front exit from the Chilton manual. Sorry so long, any help would be appreciated.
Bernie