according to my wagner master catalog, the 76-78 aspens use #PBL503800 booster[comes with a 4 bolt master cylinder]. the volare uses the same booster in 76-77, but changes to a #PBL503870 for 78-80, which the aspen also uses in some 78's and all 79-80. this is because those boosters come with a 2-bolt master cylinder. the 2 bolt booster alone is #5473870. the 4 bolt booster is not listed as available. hope this helps.