Hi everyone,
I acquired a pair of the EV MT-12 speakers on ebay sometime ago with the intention of trying them in an open baffle. Dave (Hurdy_GurdyMan) explained in another post that these are close cousins of the LS-12, (different tweeter) and liked them (the LS-12) in OB. So, I mounted the MT-12s in a baffle that I cut out from a corrugated box. Here is one of them.

The baffle is 14.5" (W) x 20" (H). Driver is mounted about 13" from the bottom, centered on the baffle. Wings are about 4", on both sides. This was not out of design: the corrugated box had flaps like that.
As to the sound, very natural and relaxed. Good bass too, probably because the drivers are so close to the floor. I do not have an SPL meter to measure, but I like what I am hearing. I think vintage drivers are a good and cheap way to go for OB experimentation.
Ashok