So I've worked with EPE and KTR (a lot):
http://www.epe.com/
http://www.ktrperformance.com/

KTR no longer does performance work, but continues to run their dyno. EPE seems to have a loyal following.

I've never used the following folks, but got a good impression from meeting the people at track events:
http://www.autobahnperformance.com/contact.htm

Any other suggestions for good independent Porsche shops located in MA?

By the way, former KTR guy has set up his own shop in Lawrence MA:
http://www.kmcauto.com/
He's currently working on my track-oriented car:
http://www.kmcauto.com/project_cars/..._M3_turbo.html
Tim is as competent and honest as I've met. (and nice too)

 

I had my PPI via EPE. Nice, competent guys.

Spot on the car's motor being a gem.

That is all I know.

JB