I used a Peavey extension cab with a Sheffield with a silver stripe Bandit I had, just sounded fuller/louder. I later built it into a cab and chassis with a Weber Thames, I found I had a little more bass this way.
I've had several Peavey "Special" amps over the years, and I still have an early 80's "Special 112" chassis waiting to go back to work. I re-cabbed the last Special 130 I had, but let it go for a nice Washburn A/E.
I like the look of piping, only tried it once on a speaker cab to match an Epi Valve Jr. head. I knew I had to leave room in the baffle dimensions, but didn't consider needing a deeper setback!
I've had Fluke for years, and after leaving the power company I was working for, I purchased a Fluke 87 to replace their 77 I had been using. That was 1990! It died a year ago, and was not repairable, so I bought a $35 unit from CE, (Antique Electronic Supply), just never could get used to it...
I'm not familiar with those rectifiers, but I do have a Weber "Copper Cap" in my DR build. I played around with it and a GZ 34, and there is very little difference in voltage. It could be because Weber designed the SS unit to more closely mimic a tube rectifier.
While I haven't heard an original 5E3 in a long time, I have built a couple. The first I used parts on hand, a DR PT and OT, and Sprague Mallory caps, and mostly carbon film resistors. I also used a Tube Depot PC board! I did a couple of switchable mods, but generally play it without those.
Seems like plenty of room to mount the tube sockets, I think I would use dedicated wiring going back together, and treat it like you would an old Fender. (You could also just use the thing as wired!)
I don't think you'll have any problems with the little tank, move it closer to the front. Before...