The 1" bore disc brake master was used from '67-'70 on A-bodies. There was no 1-1/32" bore master as original equipment on an A-body made before the 1971 model year. There is no "1970-1972" disc brake master; that's two different masters: '67-'70 with or without power, '71-'72 with or without power. Starting in '73 you had your different bore sizes for with vs. without power.