I recently dropped in some Pioneer TS-A878s in my dash- they sound great are are also a large upgrade from stock... On drivers side I cut the factory speaker bracket (as others have done) so it can be "spread" apart to accommodate a larger speaker... For passenger side I had to make a longer mounting plate but it is simple. I used a basic 100uf capacitor for a 400hz 6dB/octave high pass filter. For wiring: you can very easily use a spade connector (as shown in link below) plugged right into the factory plugs. I bought a pack from Home Depot that came with two sizes...the smaller of the two fit into the plug connectors perfectly and these also bridge the parallel connection to the door speakers.
Ring & Fork Electrical Terminals | MSCDirect.com
Ring & Fork Electrical Terminals | MSCDirect.com