Erick Henderson at www.pentaxs.com does a good job. I sent him a Spotmatic but that's little a brother to the big 6x7, right? I see at his page that he does 6x7s and I can't imagine him doing a bad job on these. My little one came back as new.
Pentax USA still accepts 6x7's for service, all except for the earliest non-MLU bodies.
Agree that Eric is also worth considering. He did a shutter repair + CLA on an MX body for me recently - the job was reasonably priced and completed within the promised time.