Is the bore bad. Get a 383 kit it will replace the crank pistons and rods for about 800 bucks.
If the block is trashed just get a good one from the junk yard or locally just make sure you can look at it first. Good blocks are not hard to find.
Some of the crate motors are so poorly built they are not even worth the time. Inwould build my own after some of the enginesi have seen i am not going crate motor again unless its all 100% new engine.