Hi Raymo,
I wish I could answer but I've never had the luck (or cash) to get my hands on an original pair of Dynasonics. I imagine you're planning on swapping the guts out of the 2K PU, that is to say, push the inner black part out to use the chrome mounting rings?
My guess is that they will fit. I have a NOS set of 2Ks and there is a tiny solder blot on each end which I'm guessing holds the actual PU in the chrome mounting ring. The only info I've ever found was here
http://www.rockabillyhall.com/soundlikecliff.html , with this fuzzy picture:
[img:448:333]http://www.rockabillyhall.com/JAslide06.jpg[/img]
Note the blurb:
DeArmond versus DeArmond versus DeArmond. Not a very good picture unfortunately, but it shows an original Rowe DeArmond (top), a Gretsch re-issue DeArmond (middle) and a Fender re-issue DeArmond (bottom). From the top all three look alike. It is evident, however, that Gretsch has made exact duplicates of the originals in construction.
Also note that if you're going for the exact look, the 2K chrome rings are notched in the side (front in pic), although I've seen many 2Ks mounted stock in Gretsch and Dearmond guitars with rectangular mounting rings and no notches. Mine came NOS in boxes as replacement PUs.
You can also try calling GFS
http://store.guitarfetish.com/vintagestyle.html suggested to me once by our illustrious site admin and fearless leader Don. They have a series that I think are meant as direct replacements for Dearmonds and Filter-trons. You may be able to purchase just the chrome rings from them.
Good luck and welcome to the forum! 8)