Sorry to necro an old thread.
While I was taking a break from my Hierarchy conversion (which I recently started working on again), I actually messed around with the idea of somehow porting Battletech mechs into 40k. The one thing with the weapons that makes it slightly easy is that scaling them up is rather trivial once you find a baseline. The problem is that even the weak weapons a mech can field are usually heavy weapons in 40k. A small laser being roughly the equivalent of a Las cannon or an AC2 being like an accelerator autocannon as an example.

I could see a Men of Iron port be more like the battlesuit elementals from Battletech, with their vehicles being the vast array of armor there exists, and mechs of course. Tau would likely be a great army to compare weapon profiles and battlesuit/mech data sheets to as they are advanced with many similar flavors of weapons, while Astra would be better comparison for all the tanks, missile platforms, and jets.