1977 corvette 350 auto new torque converter-new flywheel-new starter.

Does it spin over at the right speed, or does it sound like it's "dragging" a little?
You may have a starter designed for one particular tooth count flywheel, and a different tooth count flywheel.
If the flywheel or crank is bent, you should be able to see that on the old flywheel(if you still have it) Look at the teeth on the old flyweel. You may see that some of the teeth are worn all the way across the face of the teeth in some areas, and some teeth are only worn about halfway across. This is a good sign the flywheel is not running true, whether due to a bent wheel, or crank.
Starter grinding is a pain to solve, in some cases. There are several different flywheels that will bolt on, and at least two different starter noses. Only one combination of the two will work properly. If either have been changed in the past, it makes it even harder to figure out which one is the problem, and replacing either according to what's on it now may not solve anything if what's on it ain't right!(did that make any sense?)

If shimming doesn't help, then it may well be the wrong flyingwheel.
Does the starter you have have two different bolt patterns, like straight across, and diagonal? If it does, and the block has both patterns, you might try using the other pattern to see if it changes anything. You might think it won't matter, because "there's still the one bolt that's the same on both patterns, so how could that move the starter?", but it does. It will change the angle...
Just an idea...