You can get to 90% of the wires by taking out the dash cluster. I got rid of the wiring harness on the firewall(actually, I still have three wires to remove before it's fully gone). You might consider replacing the speedo(not the bikini kind of course
), since from what you said you're going aftermarket anyway. Also might consider sticking in a tach(since I'm guessing MS=MSD and you'll have a tach output). Also, if you have a dashpad taking it out will help to move the wiring, it helps out if you change the wiring significantly. There's a little beehive of wiring right above the cluster that I reduced the size by about half by re-routing wires, it would have been much harder to do if the dashpad would have been in. If you choose taking out the windshield be ready for a load more spending, it'll temp you to replace the windshield gasket which cost a lot, and obviousely you'll need the sealants. This wiring is so simple though I think that a complete overhaul on the wiring could be fairly easily done(you know, as far as the ease of re-wiring a car can be considered easy 
). The only compromise I could imagine would be quality of connections, getting a sauter gone in some parts of the dash would be a b**ch.