Very cool.
Buying these vintage mics off of eBay is a crapshoot. Every RFT mv692 that I have ever purchased was "calibrated, reworked and upgraded" by Peter Drefahl of
www.drefahlaudio.com. The older "noisy" mv692 RFT components were replaced and a professional conversion to XLR performed by Peter. It would have probably been just as economical to buy them new from Gefell. BTW, I also own a pair of the new, modern day mv692's.
As for the UM70's. I was able to purchase a pair of NOS UM70's that were given the two thumbs up by Peter Drefahl as a matched pair.
I did receive a few "eBay duds" in my search for UM70's which were promptly returned to the seller until I got the new, mint caps that I was looking for. If I didn't already have Grade A versions of these mics I'd certainly take a hard look at these.