I have a Schneider Symmar-S 150mm lens that has something going on inside it. It looks like the coating is coming off the internal elements. Rather than have it repaired, I have an opportunity to purchase an APO-Symmar 150mm that has a broken shutter at a very low price. The shutters are the same size, Copal 0, but if I switch out the elements, will the aperture scale be the same? Will I need to change those as well?
Not shure, but you can make 2 shots to be shure: same shutter, diferent lenses, same shot, same development.
If you don't see a density diference: you don't have to change your aperture scale.
And as both are 150's I don't think from the start.
The shutters and not least, the aperture openings, should be the same. Just be sure to check for possible shims from the Apo-Symmar lens. If there are any, see to that they are transfered to the older shutter. Apart from that you should of course do the test which archphoto suggests, as there could be a difference even though common sense says they should be the same.