I've bought EL-Nikkor 50mm f2.8 for my Meopta, only to find out it doesn't fit

I have the 39mm lensboard like this http://www.fotoimpex.de/shopen/darkr...5aax-2-4a.html which you are supposed to insert with the "bump" side up to get the proper focusing distance, but the Nikkor is to wide and doesn't fit.

I guess I'll need to custom build a lensboard.