I did this too a few weeks ago, mine had some mdf speaker mounts but they were knackered. I butchered the original speakers and used them as mountings, didn't take too long though, jigsaw and a dremel and they fit perfect
Did you use the original wiring? I found the hardest part was getting some decent speaker cable through the door plug. My system sounds awesome now though, good speakers, amped with a 10" understrut sub