Definitely Post replies you get from everyone. I'd love to answer because I use to have the Shaker 500, but I eventually changed out everything. A shop should be able to answer that question for you, but I do remember the Techs had a pain in the @$$ time when they were trying to wire around the Shaker 500 front sub Amps. They told me back then that it would be easier changing out everything but I was stubborn in the beginning.
One of my local audio shops did the swap in a 3V. They said, long story short, most of the interior has to come out; along with you butchering the wiring harnesses.
I wanted the shaker 1000 in my Roush, but not enough to justify the hassle and expense.
You're far better off just getting a sub of your choosing, one of the boxes that are designed for our trunk, and a suitable amp for your sub. Then you can just tap a rear speaker wire and use a line level converter. Easier and better quality than the Shaker stuff. Also cheaper generally (though maybe not cheaper than a junkyard find).