I believe that 1964 was the last year of the bendix gear type starter in ford. My 64 F250 has this, all thereafter use the prestolite overruning clutch type. When the motor starts and flywheel speed increases, it thrusts the gear forward to disengage, where the newer ford starters use field magnetism to pull the gear into the engaged position, similar to the way the solonoid does in on GM starters
as for what the purpose of this setup ,I dont know, I have also seen this bendix setup on a cummins V12 marine engine that was on an air starter motor. Most older auto parts salesman will tell you that years ago they sold these like hotcakes, today your local antique parts shop normally has a couple in stock, or others can order within a day or two.