for the loom try not too cut any wires, there is no need to do this, bit of a pain in the arse having to solder them together.

if in doubt , label all connectors when you disconnect them .
if the new shell has any wiring left in it at all for the roof clock and light you can attach a couple of lenghts of wire and pull through. you can the re-attach the new wiring onto this and pull through

before putting a loom in a car i tend to lay it out on the floor and strech it out, that way i can visualise where it should go when putting it in the car