I would think that without the thrust buttons ,cornering would put a tremendous amount of side load on the axle bearings.

Unless using green bearings, yes, is a must. With axles in they can't go anywhere, but the thrust buttons ( or thust block when open diff ) makes both axles keep conected keeping the axle assembly axial play with stock bearimgs being adjusted in just passenger side

I think any hardware store could get a same diameter roll pin. Is not really specific for it. Stock one gets a punched shape just to get a limit when installing but is not really needed.

The axles will be getting in and out freely no matter the adjuster position, getting bearings out of the race, damaging inner seal and whatever else related to the axial play... drums against brakes assembly plate, pads etc. aside that, when axle bearings are not set into the race correctly, the axles will be getting up and down, side to side... moving out of the center.

( I heard you on the broomstick trick, but, damn! I found hard to get the roll pin and holes matched in that way! )

I understand the thrust buttons are needed.
My question was:

Is the “roll pin” really needed, If the axles are in, where can the “thrust buttons” go?

I think you missed the point that the roll pin may get between the gears and tear it up.

Do it right.

sure, but I meant the punched shape end/head is not needed once is installed. Any roll pin fitting tight into the holes will make the job

interesting question since I have allways found it gets broken in halfs ( each half inside each button ) making work freely instead like one piece one against the other. Maybe yes maybe not... maybe is just for installation purpouse.

I have allways found the thrust buttons should be made in another way and fit tighter into the gears cross somehow. They get WAY LOT OF ROOM around once installed what mostly sure makes to break the roll pin easier. Will never understand that. Maybe thrust buttons should be made somehow being a male and female piece. Just thinking out loud