You'll get a lot of opinions on this, there is an opening for a speaker at the center of the dash, I believe it's ~5X7 but used a dual voice coil speaker for sound seperation. Problem is I haven't found any reputable speakers that are dual voice coil, just Audiovox and the like.
I'm taking my chances and mounting 2 Polk 4" or 5" on a home made panel to mount there. I plan to 'cant' them as much as I can at an angle towards the L/R to see if that helps with seperation. Won't know sound quality until I get it all installed, those in the dash, 5x7 in the door grilles (deluxe door grilles) and 6x9 in the rear shelf.
Jon
__________________ '67 Coupe 289 C4, Candyapple red w/red deluxe int., PS, ext. decor group, light group, foxbody seats.
Next to install> stroked 333, AOD, 9" w/3.50:1, PDB.
'09 Black Warriors In Pink with glass roof - the wifes Mustang.
"If it ain't broke, I haven't fixed it yet" -Jon | 
Replacement Speaker 
