75 350 starter

Can anyone help. I am putting a new starter in and does anyone know how to check the spacing between the gears. I am unable to push the starter gear forward and mesh up the two gears to check the gap between the gears.

I would just install the starter, if it sounds quiet, you're good to go. If it is noisy, loosen it up, take one screw out at a time and install a thin shim. I think the max on that was .060 thick and the shims are .030 each.

Bob