36mm from the back of the transformers to the back of the panel. Add ~2mm for panel thickness if that matters to you.
Previous diameter noted, I suppose you could always grind out clearance on the rails.
While I really like the idea of modifying modules to fit in the Intellijel 1U spaces, and have even considered/am still considering doing so with certain modules, my personal opinion is that the RIP is far too perfect even as an aesthetic object to warrant physically tampering with the panel. It’s compositional integrity would be ruined, to say nothing of the fact that the graphics would be mis-oriented (it sort of demands correct orientation). As a former surfer, my fee fees are strong on this!
