First of all, this design is a remix of the original Prusa i3 Mk3 left z-axis top mount and some ideas from ctilley79's reverse bowden design https://www.thingiverse.com/thing:2825557 .
The problem was, though, that everybody who uses the Mk3 in a reverse bowden setup outside of a box seems to feed the printer from the right. Can't do that, there's no more table there. The one left side top I found was just a reversal of the corresponding right side mod. The problem, after I printed it, was that, when printing in a high z position, the filament would have to run through the x stepper. Not good.
So I sat down and made my own. The design is currently just printing, so I have no idea how it will work in reality, but at least there'll be a little bit of clearance between the x stepper and the filament.
I'll update this description (hopefully...) once I've actually mounted that arm and routed the reverse bowden.
It's working :-)
20% 3d honeycomb - because I like it