I’ve collected a few trashed trombones to practice soldering joints and while looking at two of them I’ve formed a curiosity. The upper tuning slide legs on two of these instruments are exactly the same length and diameter. The bells are much different lengths. I haven’t yet done this, but if I swapped the bells should I expect a noticeable difference in how in tune they play? The dimensions of the bells otherwise are also much different. Assuming I can get the slides in playable order with just a makeshift jig and a surprisingly level table.

There is no standard length for a slide section or a bell section. If you swap the slides to different bells you may find a big tuning difference. Measuring the overall length of the slide with a tape measure (i.e. right along all the tubing) can help you predict the combination.