I added some new disk brakes to front of my 68 Chevelle, rear are drums. I went to bleed brake lines after bench bleeding master cyclinder and found that I had no fluid going to the rear. I then disconnected the rear line at the MC and put on a clear rubber hose to check if fluid is exiting the MC and found it was not. I feel that the plunger rod (longest one provided used from the kit) in the booster is not actuating the MC to provide fluid to the front or the rear, although I have not checked the front yet. I am thinking of adding an extension to the brake pedal that was provided with the new Stainless Steel brake kit to make the action through to the plunger rod long enough to actuate the MC. (currently the brake pedal seems firm and in the correct position) Does this sound logical to extend the brake pedal rod to solve this problem or am I missing something here?

I would advise you to check the clearance between the MC and the rod from the booster first. You should have around 1/16" free play. You can use a piece of modeling clay to do that. Only after determining the play is excessive would I go to the longer rod.

I need an extension for mine. What's this thing look like?

I actually bled the front calipers first and that seems to have built up enough pressure in the front brakes to start the fluid going to the rears. I'm not sure why this worked but I essentially ended up bleeding them all in the opposite order that they should be done which got the air out and the fluid to where I needed it. I'll have to go back and do them in the proper order now...from furthest away from MC to closest to do things properly but at least the fluids flowing and the pedal seems to be quite firm. Can't wait to try them at an hour that would be acceptable to the neighbors.

Once the air is out, it doesn't matter what order you go in.

Besides, according to my factory service manual, you bleed the fronts first anyway. I think it's for the very reason you stated, to build up hydraulic pressure in the secondary circuit first (because it has the weaker return spring).

You should still verify the pushrod length, and never use the booster pushrod to effect the master pushrod. It just will make the brakes want to drag, or even apply by themselves when you start the car.