Newbie questions.

[LintMan]

I've never seen a "sizes must match" message, and my upgrades regularly have different #'s of components.

Are you maybe seeing the "maximum 50% cost difference" message? If you are, that means that you new design costs more than twice as much as your old one and you can't upgrade that ship to the new type. (Actually, you can if you're willing to design intermediate cost level designs and put the ship through a series of upgrades - very pricey!).

You can adjust the 50% number through a setting in Settings.txt.