Not as difficult as I first thought. If you make a few adapters up to get round the problem of getting into the doors then you'll be fine, will be a bit more complicated if your not amping them.
Basically what i've done is i've got a feed from the amp in the back up to the front and up into the dash where it connects to the crossover, from there the tweeters are mounted in the oem locations and have new wire running from the crossover to the tweeter in the dash. Then what i've done is buy an unwired iso plug off ebay and solder fork plugs onto the ends of the cable, then connected this to the crossover for the mid output.
So it uses to existing loom to get to the mid in the door and fresh wire ran across the dash for the tweeters, will be fine unless your intending to stick silly power through them as the original loom is probably only good for about 50-60 watts.
Dash top is easy to get off, three screws in the screen heater vents, one behind the silver trim on the drivers side, three under the silver trim passenger side, two under the top steering cowling and one either end of the dash.