the cnc´d version of the 360-1s are often leakers in the exhaust port as far as i know. I did some research because i want to run a set on my car, just bought a new, unmolested set that will be ported at IMM engine. Swap is planned during winter time, so no results at the moment.
I have been told that the new owners have adjusted the cnc program and fixed the problem. And I know a couple of people who purchased the un ported and had someone else port them. They turned out good as well.