Both fixures were typically added during the earlier, SCB-27 (Korean-War Era, still straight-decked) refits. And you're right that guns were continually removed as time progressed - however, bear in mind the single-5"ers were the last to go. What I think you're looking at there is a 5" moved into a (reinforced) tub, displacing an earlier twin-3"50cal - probably during her SCB-125 (angled-deck) refit.
As for your actual, hollow bridge idea, that is indeed possible - and exactly how my Boxer bridges (both of them) started out. I can upload some pic(s) to show you (if I don't space out on it ). But it was extremely time-consuming - and I have future Essex builds planned, which is why I pursued the idea of a molded one. (Nowadays, in fact I could produce a molded and hollow bridge, come to think of it!)
I checked and do indeed have more of those original fantail moldings available for you, anytime, Kevin. As always, thanks for the compliments.
And that's a great job you're doing on your Wasp - keep those updates comin', buddy!