Unfortunately, when building up a motor from an assortment of aftermarket parts, one can't expect things to fit together like Legos. That being said, I too ran into some quality issues that surprised and frustrated me. It can be a very trying experience, especially when you take the time to actually do a good job, rather than just bolting the stuff together. Just as an example, the
oil slinger at the rear of my SCAT crank was actually to big and it bound in its corresponding relief slot in my block. I had to have it turned down on a lathe. The main bearing bores of my block were quite out of round when I first got it. And that was after it was supposedly align bored. And the list goes on. That's the way it is. The only people who haven't had these sorts of problems are the ones who don't check.
As far as the barstock key, I did have to file it to fit into the crank. I also had to have my spacer honed AND I had to massage the slot in the spacer to get the whole mess to fit together.
phil