my bud took a head out of a mkII 2x12 combo and made a head out of it. Epic. 40 watts, so much better.

Either taking the 'head' out of a 112 or 212 combo and putting in in a head cabinet or using the combo in conjunction with an external speaker box is just fine as long as proper impedance is observed (and plugging into the proper output of the amp as mentioned above).  I just picked me up a Boogie 1x12 theile cab (the newer ~23" wide) to stack my 112 on top of and I'm liking it very much.  I haven't had a chance to play out with it yet, but I've played it at proper club levels and like the extra thump added with the theile cab.  Technically the setup won't be any louder (i.e. 40 watts is 40 watts), but the sound will be fuller and you will have more presence because you're moving more air.  FWIW I purposely got the theile cab with a C90 speaker in it for variety and have a spare EVM12L to pop in, which I was going to do immediately but I'm kind of liking the mix of the 2 speakers right now.  I have an EVM in my 112 combo.  One thing to keep in mind is the effeciency of the speakers you use.  I'd be willing to bet the overall loudness with the EVM in the theile (vs the C90 in the theile) would be a tad louder because the EVM is more efficient than the C90, but only a tad as again 40 watts is 40 watts.