The booster mounts with a 4-bolt pattern. The 4 bolts are in a perfect square and are 3 3/8" apart (center to center). This Kit is designed to work with your 1955 1956 1957 Chevy Tri-Five Car including the Bel Air, 150 and 210.
1955 56 57 CHEVY 210 BEL AIR REAR 1" DROP LOWERING BLOCKS U BOLTS COMPLETE KIT
1955 56 57 Chevy 8" Dual Brake Booster + Master Cylinder & Bracket Kit DISC DISC
1955 56 57 Chevy 8" Dual Brake Booster + Master Cylinder & Bracket Kit DRUM DRUM
1955 56 57 Chevy Tri 5 Chrome Power Brake Booster Master Cylinder Disc Disc Kit
1955 56 57 Chevy Tri 5 Bel Air 150 210 Brake Booster Firewall Mounting Bracket