I did not do any test yet, but since you guys are very cooperative:
Thanks for the offer. If my tests do not show anything, I will take it;
Looking at the lens it looks fine, and enlargements (did not do a side to side compare) are fine;
No, technically I did not have to. That's one of the reasons I've bought the Nikkor - it has the same flange to negative distance of the 50mm (but the glass protudes more in the back, so it's really closer to the neg).
And thanks also for all other posts.