Edit: Sept 24, 2012 added rear speaker pics. If you don't see them then refresh the page.
A quick way to mount two 3-1/2" speakers in the front where 1 am speaker was using the am speaker mounting plate and scrap wood.
I changed my plan back to the original am speaker cut out with a 4" grinder.
Cut through in no time after using a cardboard template of the dia of the speaker top marked with a sharpie.
A black T shirt was used for the cover and held in place with fiberglass tape.
6 x 9