The shim is used to establish the .76” clearance between the frame and the bottom of the floor shown in red arrows in the photo. Using the block of wood I talked about helps get you determine the thickness of the shim.
Have you checked the front mounts? They also have an effect the rear mounts.
Last edited by Phak1; 01/03/20241:07 PM.
Phil Moderator, The Engine Shop, Interiors and Project Journals
1952 Chevrolet 3100, Three on the Tree, 4:11 torque tube Updated to: ‘59 235 w/hydraulic lifters, 12v w/alternator, HEI, PCV and Power front Disc Brakes Project Journals Stovebolt Gallery Forum