Never heard of them. Two places I can highly recommend from experience:
Automotive Techniques in Novi. Run by Jeff Jones who was a Porsche tech during the 944 era; really does know these cars inside out.
Arbormotion in Ann Arbor. All the Porsche stuff is handled by Tim Pott. Simmilar story there, he really does know Porsches of this era.
You can find ads and contact info for each in the local PCA newsletter:
http://rsp.pca.org/BahnStormer/Bahn_2017_10_web.pdf