Wow. More responses than I expected. Thanks to all of you!

Mr Salomon: Eminently sensible suggestion. I tried it, and indeed the level is level. Which is pretty much what I expected.

Mr Sampson: Yep, the Ektar is a coated Anastigmat. I've been using the Anastigmat for black and white and it's really just fine. Just can't aim it at the sun.

pepeguitarra: Yes, I believe they are interchangeable, since the design of the lens elements was apparently not changed. Just wanted to see if anyone knew of any specific reason to doubt that.

Mr Scudder and Tin Can: That's kind of what I was afraid of; and if it's true, the variations would likely be too small to be revealed by measuring with a level. I suspect it's not the case with the very mass produced 203mm, though. Maybe with some of the higher-end Commercial Ektars.
I am a long time fan of Ms Flutot, and I'm on her waiting list, but she has serious family problems and says her shutter work is going very slowly. I wish her the best.

Regarding repair of the dead shutter: That's part of the "long story" I referred to. Way too involved to go into here, and not very interesting.

Mr Lindquist: Thanks for the Henry Paine link. I'm always on the lookout for shutter repair technicians; they're a rare breed and getting rarer. I was disappointed to learn that S.K.Grimes, for instance, is no longer doing shutter repairs.
Oh, and I'm in Michigan, which is still part of North America. ;-)

In any case, thanks again to everyone. I think that more than answers my question.