My colleague has sent 4 87ais to Klaus Heyne. It was worth every penny and I don't say that lightly. When the first 2 came back we tested them against the other stock ones which used to be quite similar sounding. With gain matched it was NOT subtle. The new mics were HUGE and detailed. Their output was hotter. He transformed a "decent on most things" mic into a very high end beast. Also each of the 4 mics now have a modestly different character so we have a broader palette to choose from as well.
I can't imagine a more satisfying transformation. When I next buy some 87s, the dealer will be shipping them directly to Mr. Heyne.
Best,
Silas