You cannot bend an EV frame, it's cast iron.
EVM12L's will fit where there are Celestion or Eminence speakers studs or holes, at least with Mesa cabinets with the OEM studs. I switch around speakers quite a bit and my most recent thing is a Rectifier cabinet with 16 ohms on one side, 8 ohms or the other with EV & celestion mix.
4 screws are not enough! You must use 8 screws or it will rip out, trust me, I own and use them bastards.
Wattage has zero effect on a speaker as far as sounding good at low volume, it does not need more speed, hp or energy. That's not how speakers work. EV's sound terrific at bedroom volume, smooth as fuck.