@For_Science Absolutely
It's going to connect to the bottom of the MJOLNIR, i.e. the back plate on the Core (the one with the power button) will be replaced with the BORG, then the conversion is done. BORG has it's own dedicated power button on the front and an opening for cables on the back. Now, say that you make the MJOLNIR vertical and want to flip the internal layout (GPU and CPU sides switch place), this would rotate the BORG as well and make it so the power button is on the back and cables are sticking out the front...not nice, so we made sure the middle part of the BORG (the one that connects to the Core) can be rotated as well. Last, it works with any MJOLNIR thus far (Kickstarter, Batch 1, 2, 3 and the upcoming 4 of course).
As for thermals, this will be the most optimal way to run MJOLNIR (unless you have a blower style GPU) because there's very little resistance on any side. So for those looking for the best performance it's MJOLNIR w. Performance panels, 2x O2 panels, Booster Cell and BORG.