Why would you want to slice+dice an expensive floorstander like that instead of just trying a VP150 that's designed out of the box for that sort of deployment?
If you put an M80 on its side and perform surgery, you don't really still have an M80 when you're done, so you're not at all achieving the goal of matching M80 L/R mains.
Most people who can use a full-size floorstander as a center seem to be using large front projection screens mounted high.
Note that the idea that ideally having identical L/C/R speakers doesn't mean that a different center solution will suck -- there's a certain amount of diminishing returns effect here.
Conventional wisdom is that video/movies (which is what most people want a center for) mix mostly dialog into the center channel, which is concentrated in the midrange. The bass and treble extremes are much less taxed, which is one reason why you'll find a number of people who are happily using smaller, bookshelf speakers for centers, that can perhaps be inserted into a stand or placed unobtrusively in front of it - or even in front of the display on the top shelf of the stand, or on top of the display. Several happy reports of M2 centers can be found on these forums.
My plan if I ever navigate the WAF for my system is to order a VP150, an M22, and an M2 to see what works best with M80's and QS8's, and send back whichever I don't decide to keep.
