Caution against the 1" spacer idea.....your speakers will hit the edge of the back seats with the seats up or folded down. Don't use any more than a 1/2" thick spacer, that's cutting it close as it is. And you're not going to be able to use the stock grills....time for some customizing and fabrication.
Best bet, IMO, if you need to use a spacer...
I ordered 1/2" molded plastic spacers from Uneek Supply and they were a whopping $10 including shipping. They're on ebay or you can call them directly and buy them. Throw away the fasteners included for attaching the spacers to the door panels...some screws and those tin speed metal nuts. Get some real nuts and bolts.... phillips head #10 x 1-1/2" machine screws, washers and nuts. Bolt the spacer to the door panel, then screw the speaker into the spacer with regular sheet metal screws. That's a rock solid mount.