You might want to consider
Kraftwerks (
Kraftwerks Performance - Independent Porsche Specialists)---that's where I'm leaning towards going to for the IMSB work. They're just outside of Columbus. I emailed them, asking questions about the whole process. Got a response from a guy named Jeff Brubaker. Among other things, he told me:
"We use LN Engineering products for the various M96 engine upgrades. Their IMS is by far the highest quality on the market. Typically you will want to do the clutch kit, the IMS retro fit, and the RMS replacement all at the same time....We have done a few upgrades already; however, I believe we are the only ones in the area to have attended the 3 day training class at Flat 6 Innovations presented by Jake Raby and Charles Navarro of LN Engineering, and been directly trained on their methods and equipment."
This was almost a year ago (my clutch still seems good, so I haven't jumped into getting the upgrade done just yet), so odds are decent they've done a few more in the meantime.
Another option I've considered is
Layland Motors, in Canton. At the recommendation of another 986forum member (who does a lot of his own work, some of it pretty major, and only went to Layland when he got stumped on something) I took my car there and got good service (replacing/repacking rear axle boots) at a fair price. I got a quote from them on the IMSB work, so they've apparently done some.