My experience was similar in my 68 Notch,340, original K. To minimize dimpling the brand new Doug's I ground the Borgeson box, and shimmed the engine towards passenger side 1/4", (I then had to completely rework the air cleaner hole in my plenum!). I still need to dimple driver side header @ T bar. I had the driver side header in and out probably 10 times through this process. Hated the thought of dimpling but no choice, I chose a large socket covered in a thick towel for the dimpling. All of this worth it for good long tube headers.