1995 Chevy Truck Will not start

I have a 1995 chevy 350 v8 5.7L. It is completely just rebuilt. We put it back in and it started but ran really rough. We found out that the problem with rough running was spark plugs and a distriburtor cap. We fixed that problem but then started having issues with the starter. It kept grinding and wouldn't turn over the engine like it wasn't engaging the flex plate. We got a new starter and shimmed it accordingly until it worked. For a short time it worked fine but then when I turned over the key the engine would crank but not start like it wasn't firing. It has new plugs and distributor cap and rotor and all plugs are gapped.035. The plugs were also very dry inside after pulling them out. As soon as we started diagnosing this problem, the starter starting grinding and acting up again. Assuming we could get the starter to work again, what would be the next step in troubleshooting why the engine won't start? Any help is appreciated. Thanks