A 7" driver would probably need some decent modification to the composite door panel. Many of the cutout diameters for 7" drivers are larger than what you can enlarge the stock speaker opening to accomodate.
The 6.5" driver from my Rainbow Germaniums required modifying the stock opening slightly (had to enlarge it .25-.375"), even with the driver mounted on a .5" MDF baffle. This was very easily accomplished with the handy, dandy, Dremel.
As far as speaker adapters, if you have access to jigsaw and/or router, just pick up some MDF at Lowe's or wherever and make them yourself.