Are you sure that you can get a 73-77 drum brake set up? I'm fairly sure everything in that era was disc/drum. I also question that this booster would fit under the floor. As 53chev says there are some physical differences but the main internal difference in the disc/drum and drum/drum master cylinders is the residual valve(s).
Fred

1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine