Board Thread:Unanswered Questions/@comment-75.95.173.188-20150423000614/@comment-25045164-20150423013443

Short answer: Yes.

Long answer: If you can equip a weapon-specific Part for a SPW that you've fitted on a plane, then its upgrade is applied. Otherwise, the game will gray the Part out and won't let you equip it. I have UGB upgrades loaded onto my bomber myself.