Early footpegs were two pieces silver soldered together: the spindle and the footrest. You can sweat out the old spindle and replace it if it isn't too deformed.
The early parts book lists the two parts, but the illustration only shows the assembled unit.
The early units were silver soldered, rough cast and nickel plated.
The later units were bolted up, smooth cast, and chrome plated.
You can bolt up a newer threaded spindle to an older casting, but the casting is not threaded so you need a nut on the inside. And the boss on the early casting is smaller than on the later casting, making it a weaker as a bolted assembly.
The rivet counters will notice if you swap the early for the late castings: proceed with caution.......