P/S box question

Slightly o/t but hopefully someone can help.

A friend is looking for a power steer box for his Challenger. I seem to recall Mopar p/s boxes are pretty much interchangeable all the way from the early '60s into the '80s except for differences in output shaft and possibly input shaft?

My friend's got a Pitman arm for a 1 1/8" output shaft - is that large or small?

Are there differences in the input shaft and which would he need - it's a '73 Challenger btw.

Thanks