more brake help, booster rod length

[veltex]

Hey, I am switching to disc in front, from power drum, the booster rod seems long for the new disc master? I can put the master on but have to push in hard then bolt down like the rod is longer for power drum than power disc? and then there isnt much pedal travel like the master is already most of the way in, the rod has a threaded end that looks like it may adjust shorter a 1/2 inch, and the pedal rod may shorten a little less than that, anyone dealt with this before? If its adjustable, how do you know when you have it right? Do I need a new rod? The power drum booster will work right? thanks