Do later model A-body masters need the dust boot the earlier ones came with. I noticed during my disc brake swap, the 73-up master doesn't have a provision for a dust boot. Is that a problem???
this is what my 75 duster used. just plastic with a lip to hold the boot. I grabbed one last time I was in a yard to replace this cracked one. (the one I got was still cracked a little by one bolt) Probably most of them are cracked cause you gotta pop the pusher shaft out without hitting this brittle plastic.
I can't imagine a missing boot causing any problems unless your car's interior is messy, say a surfer who tracks sand in from the beach. They had to design for worst-case usage. I would be more concerned with power brakes where the rod entering the booster is in the nastier engine compartment.