Excellent choice of project. Have you joined the club and downloaded all the manuals? There is pretty much everything you could need and in the old selection of newsletters some good guides about maintainance and problems other people have worked through. There is also an alternative parts guide for bits and pieces.
1. Has yours got the transfer box? If so what is wrong with it? This is one of the only bits of the UMM (apart from the body panels) that you can’t get from anywhere else. I believe the chain inside it is made just for this application too and some strange dimensions that you won’t find elsewhere.
2. Which bit of the heater? The hot/cold lever switch is from a renault 4 or 5 I believe – again information gleaned from the pdfs of old club mags/parts guide.
3. Dashboard bits all Peugeot 505 I believe.
ps. drop me a pm with your email, I have some stuff to send