I would go beyond a mag. Have it sonic checked and the crank saddles checked and align honed as well. I just had a 176 mile engine in my Shelby start putting coolant in the oil. I had to pull it and sleeve #6. Sadly, core shift, corrosion or incompetent machinist can cause a myriad of issues. It's no minor task to pull an FE with headers, especially post a 15K paint job. Do NOT short cut anything.
-Keith