I have a '48 B4, restored and set up by Epiphone maven Wendy (Mollykay on the Forum) and Lonnie of Bass Monkey. It had on a set of Spiro weichs when I got it, but I soon switched those for Gamut gut. It's now wearing Innovation Super Silvers, which are a good substitute for the Gamuts. (I burned through two sets of Gamut G/As in a little over two years, and can't afford a third go 'round, no matter how good they sound.) Bass Monkey throughly documented the restoration of my B4 #1454
in their blog.
My Epi has a thin, 3-ply top -- I suspect yours does, too. The top on mine has not collapsed, exactly, but it has sunken noticeably. According to Wendy, this is common. Yours sound to be in better condition, but I know I wouldn't feel comfortable with anything stronger than the weichs on my old girl, which is why she remains set up for old-time slappin', with low tension/high action.
In fact, I recently bought another bass to have a high-tension/low-action alternative, mostly for Bluegrass jamming. That one's a Lemur Jupiter strung with Spiro reds. But that's another thread . . .