Yes, did you manage to keep the lens alignment this way? It's a homebuilt modification, with carbon fiber or what is it? I now have a couple of lens cones, one of them is quite long, so hopefully I won't need this for my 190/210mm.
Why would you need a 190/210mm, the D2 is a 4"x5" format enlarger for which you only need a 150mm?
As you can see, for the 150mm, I used a threaded rod to mount the lens flange on the cone, by this I could carefully trim the distance by less than a mm.
Then I cut a pice of PVC evacuation tube, trimmed it with sand paper, blackened, and put is in between the flange and the cone...
The other one, for the 80mm, is made of black Acrylic glass, because it was what I had at hand and is so easy to be worked on, and is sturdy enough!
The lens flange is mounted with threaded rods too, to keep it simple...
I had to put something in between the 50mm lens and the plate as that lens stack out too far and so I couldn't slide it in the lens holder. Again I used Acrylic glass, a threaded rod and some washers to trim...
Be aware: a caliper comes in very handy, actually, it's paramount!