[68PanelTruck]

I think I figured out how I can put the axle back in without taking the carrier out. I tried this out last night to see if it would work. I cleaned up the splined end of the axle where the thrust button would contact once the axle is in place. I cleaned it up with brake cleaner and glued the button to it with gel Gorilla glue (Krazy glue). I waited about an hour to set up and slid the axle in place. It went all the way in but needed a few taps to seat it in place, probably because the roll pin was a little snug sliding in to the button on the opposite axle. It worked!
This is all just a test because I'm waiting on axle seals and will have to do this again once I get the parts. I disassembled the axle again and sure enough the button was still glued the the end of the axle.

I did pull the cover off and you can't see the parts because they are hidden in the center of the carrier. I'll add a few pics of a similar setup. The cross shafts fit together and form a + Where the cross shafts meet, there is a hole drilled where the two thrust buttons fit end to end held together with a roll pin. The face of each button touches the axle shaft inserted into the carrier. The end play is adjusted by tightening or loosening an adjuster on the right side brake backing plate/axle end flange. The end play is adjusted and locked down with a clamp. Since the axles touch in the middle through the thrust buttons, both axles endplay is adjusted at the same time.

What I think happened was that after 50+ years the roll pin connecting the two buttons together loosened up and when I pulled the axle out the button fell out too. I think when the carrier was originally put together on a bench the roll pin was tight and held the buttons in place. Once the axles are in place there is no where for the buttons to move. I think in my case the Krazy glue will eventually give out but the axle will be all together and won't be a problem.