I have a 2001 grand marquis with 5x7 speakers all around, including the back.i just recently bought some 6x9 speakers and want to install them.I have went to a couple of 2 audio shops and they said something about cutting to make it fit.I have read some things and I thought that marquis come with a 6x9 adapter plate in case u ever want to adjust to a bigger size speaker.Is it true about what they saying about the cutting or are they trying to make some extra money on the side.

Been there you will still have to cut.

This can be done without cutting. I had a set of pioneer 6x9 (2 way) and stuffed them into the existing hole. You will need to drill.

Here is how it was done:
1) remove old speakers (duh)
2) hold new ones against hole from the bottom side (inside trunk)
3) position new speakers, drill new holes for mounting screws
(I used bolts with spring washer to keep it tight)
4) I also used 1/2 inch weatherstrip (foam rubber from home depot) around the edges of the speaker, position this on the edges
5) return speakers to mounting bolt/screws
6) tighten
7) connect wires.

For the wiring, I used barrel connectors, the factory harness was not transferable to the new speaker (at least for mine). Polarity of the wiring can be found at this website
http://www.modifiedlife.com/2001-mercury-grand-marquis-car-radio-wiring-guide/

Connect them up and enjoy.

Sorry about this being late, this was a question I had as well, but I replaced the speakers today about an hour ago. The entire job took about 3 hours, no dremel, no cutting, just 8 new holes, 8 bolts/washers/spring washers/nuts.

Since 5x7 speakers are smaller than 6x9 speakers, I would say that cutting would be necessary for putting the larger speakers in.

However, I have never done this, so you may be right about an adapter plate being available for the larger sized speaker. Try ebay.com to see if such a thing is available on the market (adapter plate).