starter grind after new flexplate installed

[Shellyarrowsmith]

I have recently installed new flexplate on my 69 C10 pickup and have had a consistent problem with the starter grinding. Recently I have dropped the tranny to ensure the flexplate is installed correctly, shimmed and unshimmed shimmed again the starter and am completely stumped! The starter seems really tight although running with 2 shims. I wonder if any one has any other insite on what to do next? The starter is a bosch, the engine was pulled on original installation of flexplate.