Soft brake pedal, not quite the same as other issues

[earl84]

Sorry this is so long, but I could use some assistance.
I have read many times about switching from manual to power brakes and the associated change in leverage from the old pedal and moving it down an inch or so, and also getting the pushrod correct length on the piece that pushes into the master cylinder. So I have done my research, and don't think I am asking the same question.
I have a 66 C20 that had power non-disc brakes up front and non-disc in the rear. I swapped the entire front crossmember from a '79 C20 and the non-disc 14 bolt from the same truck. Bought a new master cylinder and installed it onto the existing booster (which is pretty new and worked fine prior to the crossmember and associated disc brake swap). I have pressure bled the brakes and used my assistant (aka daughter) to do the two person method. No more air, I am quite confident. Did pretty meticulous work to get the pushrod that engages the master cylinder to the correct depth. I really don't think I need to move the pushrod on the brake pedal any lower, since I am using the same brake booster, only changed the master cylinder.
The brakes are soft and not very effective. Wanted to take out on the road for the first time in over a year, but didn't dare go over about 20 MPH. I did take it around the neighborhood, and it was awesome.
Can this be as simple a fix as lengthening the pushrod on the brake pedal? Gonna go try that, but does anyone have any other thoughts? Please read the above, I know it is long, but I have paid attention to the usual suspects already.