The 741 and 742 3rd members were started before '65 so they were also used with axle nut rears. Those early axles used shims to set the axle end play instead of the adjustable bearing retainer. Those early axles were an 1/8" different in length depending if they had a sure grip or not. The later 3rd members used the same thickness thrust block setup so you could use the same length axles. Some of the early ones may be a bolt-in with the later axles but some won't work because you can't get the end play set correctly. You would either have to change the axle shaft length or change/modify the thrust block assy.