I recently rehoused the MC-90 in my Combo into a homemade Diagonal 2x12 cabinet. I went with a V-30 for the other speaker, and so far I love it. It sounds WAY bigger than the Combo did on its own. And by bigger I don't necessarily mean a big increase in volume, its more in the way that the cabinet fills out the room with sound, it sounds much fuller and wider than the combo.
Because the MC-90 is known for having a lot of low end, I went ahead and placed it on the Bottom and I placed the V-30 in the Top position. This seemed like the best configuration, so that the speaker with the most audible Mid-range would be higher up off the ground. I may swap them at some point to see which configuration I like best, but right now I am really enjoying the sound. It seems like having the mix-matched speakers in the cabinet also did a lot of EQ work for me. I don't find that I need another EQ in the loop now, or at least I don't need it in order to get a tone that I really enjoy.