I believe you can get away with very convincing killer setup if you use the Line6 PodXT and the amp sims with something like a Motion Sound Keyboard amp, especially their Rotary Speaker versions:
Bad-ass sound, plus a full on Leslie-like rotor effect and variable preamps equals killer guitar setup most people won't be able to tell you're playing a keyboard amp with.
I believe Tech21 makes a Power something that is just a straight active cab which you can run amp sim pedals correctly through. Plus I believe if you get a good passive cab and pair it up with a very clean power amp (not a guitar head) you can get a reasonable or transparent sound.