Oz, if he uses 3 way comps, where is the midbass going to sit?
Tornado you would need to mount the tweeters in your dash locations, the midrange in the doors and the midbass (most likely a 6.5" speaker) somewhere else in the door, or fabricatr the door pockets to put 6.5" in the doors, the 5.25" midrange in a fibre glass kickbuild.
Personally, I would go for the JBL suggestion that Joe says, no messing about apart from sourcing the speaker grills for the doorpockets
Running speaker cable to the back (if there isn't any) is easy and putting standard sized speakers in the rear locations takes 5 minutes or so.