Keith - First off, Welcome to Stovebolt!
I'm looking to try and help you out with info I can pull/post from original Chevrolet Shop manuals and parts books (and any other sources I can scare up). It would help us answer your question if you could take/post pictures of your frame and cab mount areas so we can see the "three" mounting points you are referring to please.
Reason I ask this is everything I've come across so far shows there are 4 mounts per cab side, so it will help us figure out better by seeing what you can see.
