First of all thanks
@scopus for sending me original CM feedhorn. I had several flanges (mostly from old flange LNBs) which I thought will fit perfectly to the feedhorn, but found out that not all of them can be ideally connected to CM flange by all 8 screws. Nevertheless, several of them matched. Moreover, for my project 4 screws are more than enough. So, project was about adopting IBU single and twin to CM and Prodelin feedhorns and make LNBs interchangeable between feedhorns. Ideally I wanted to standardize OD of both feedhorns, but did not succeed in that. It is impossible to reduce flanges to 40mm (to use in standart Ku-band holder). So 48-50mm OD would be optimal in case of both flanges (CM and Prodelin) then same LNB holder could be used.
But the main issue, IMHO again, is the fact that Prodelin feedhorn has slightly bigger waveguide diameter than most nowadays LNBs have. So when LNB like IBU is used then the end of waveguide of it should be corrected to match waveguide of the feedhorn.
Well, I stripped LNBs, cut their feedhorns off, made waveguides OD ~21mm, and there you go- new flanges attached to feedhorns symmetrically, just stick LNB inside, tighten couple of grub-screws and test the reception. I am sure that distance from flange to the reception sensors inside the LNB is very important. But, unfortunately, in case if IBU single this distance is almost not possible to change (perhaps 1-3mm). In case of IBU twin, there are some ~50mm of waveguide which can be cut away. If somebody have clear understandig about needed distance, please tell it.
I will not be able to do reception tests as those LNBs will be sent to friend of mine tomorrow. Hopefully he will give feedback to me, then I will copy to you all.