Mr. Gasket Ultra-Seal Valve Cover Gaskets - Cork, Rubber w/ Steel Core - SB Chevy - Center Bolt 9510D The trailing arm holes are

The trailing arm holes are threaded 3/4-10 and the shock mounts are 1/2-13

Holley Street Avenger Model 4150 Carburetor

All the parts you need for a complete rebuild on your Holley carb

GM 10 Bolt

Mr. Gasket Ultra-Seal Valve Cover Gaskets - Cork, Rubber w/ Steel Core - SB Chevy - Center Bolt 9510D The trailing arm holes areUltra Seal' Ultra 20 material swells to a controlled thickness for a tight seal. It will not contract or need re torquing. a black latex coating helps create a tight seal and assures easy removal. High tensile strength improves performance. Fits 1987 96 305 350 TPI & 1992 96 350 LT1 with center hold down valve covers. Vehicle Applications: 1989 1991 Chevrolet V3500 1987 1987 Chevrolet V10 1992 1995 GMC C2500 Suburban 1987 1994 Chevrolet Blazer 1992