While lenses ARE interchangeable,
they are not necessarily aligned when you have changed them.

Furthermore, fine focussing with the 23c is not as accurate with a
50mm lens as it is with a 75 or 100. The focus gears are too coarse
to fine focus a 50, and most folks have to adjust the enlarger pretty carefully
to get the most from it.

On the other hand, you can probably get really good 6x8 prints from 35 without knocking yourself out.
11x14s will be a bit of a trial. BUT if you put just a touch of lapping compound on the gears,
work it gently, and clean it, you'll improve its personality a LOT.


Old timers often used an adjustable lens board to fully align the lens on a Beseler enlarger, and Fred Picker used to sell them. Cap screws work well. I made lots of them, and either 3 or 4 screws work well.

It looks like this:

.