Would it be possible to reinforce the 800D back to or even above its former strength?
You do seem to be quite talented, so maybe there's a feasible way to achieve this.
I'm assuming that a large part of the lost rigidity is due to the M/B tray. I noticed that
quite strongly when I disassembled my R4 for ZEUS. Cases which are not inherently
designed for a M/B tray usually use the M/B mounting plate for structural rigidity (which
makes sense of course, I'd do the same thing if I was engineering these cases).
Looking at my Caselabs a lot of its rigidity simply comes from
- thick material
- lots and lots of screws to hold everything together
- clever ways of making the parts fit together
If you want I could provide you with some detailed structural shots of the case, maybe
you could use that for inspiration? Also, could you provide some overview shots of your
system (M/B side and the back side)? It would allow us to get a better impression of its
current structural state so we'd be able to help better (I hope

).
Simply thinking about what could be done without having a detailed look at the case's
current state I'm thinking that you might have to add a replacement for the lost M/B
tray, either with an additional metal plate or maybe with some struts in the right places
(you know, like a
truss).
If you really
want to have the second case bolted to the first one then of course
go for it, it's your build after all. And just because double wide cases are not really
my taste doesn't mean you can't do awesome workmanship and impress us with
some creative metal work. It
could turn out awesome for all I know.