READ FIRST - This is by no means a complete how-to on a 16v g60 conversion. This is just advice and guidance. We are not legally responsible for the information that is contained here. If through the process you come up with any further advice please forward it to us so that we can add it to this list.
The best source of info on this conversion is the 16vg60 group on yahoo http://autos.groups.yahoo.com/group/16vG60/
I'm going on the assumption that you have a 16v (with alt, dist, exhaust manifold) and a G60 engine with charger, bracket, tubing and digifant)
1) alt doesn't fit in stock location. You have to options here, under the G60 or on the back of the block. I chose to do it under the G60, I recommend doing in on the back of the block, it's a real pain in the arse to try and get in under the G60, there is no room. You will need 2 mounting pieces for the back of the head/rear motor mount. Here are the specs for one of them, the other just comes straight up from the rear motor mount.