I had much the same angle problem with the Axiom front rack on my machine, as it used U-bolts as well. I had to make new holes to attach one end of the bolts to and they still weren't level, but at least not dangerously tilted. Just dangerous in another form.
Persisted in messing around with the enclosed attachment hardware and rigged a stable extension to almost perfectly level the bags! Bags and bike in diff locations, so pics in unknown future.