ive been thinking about making it easy for myself, grab the grinder, cut right next to the dash and pop the newly made panels off, put some weather stripping or something there and put the new speaker panels back on, it really is a PITA to get to
It's 4x6 but you have to get speakers that are flush when bottom-mounted. There can be no tweeter protrusion. If you already have speakers that will protrude when bottom mounted, you must get enough washers or some form of spacer to prevent contact... just like TwistedCopper said. And yes... they are a PITA.
I suggest buying a quality pair so that you don't have to do it again for 5 or more years. Get rubber surround and polypropylene cones.