http://www.rallispec.com/downloads/Tran ... Public.pdf
Check out this list might be helpful in finding a car with the ratio and LSD type you want it even gives you the part number of the diff, it looks like there is quiete a few options in the r160.
From my understanding the type of LSD doesn't have any bearing on how hard the conversion is. So long as your input shafts are the correct spline the diff will bolt in. You would also need to find a way of getting the tailshaft flange to match the new diffs flange as well . (If I'm wrong please on of you datto guru's correct me!)
If you decide to go R180 which is what I'm going to do, you will need the billet input shafts.
I'd say do a bit of reading on the different LSD types available and the different driving characteristics they have and pick what sounds better for your type of driving, from what you have said though, viscous would be fine but I think Clutch type is generally preferred by most people.
Apparently my 1600 has a r160 out of a SSS 200B with a 4.11 ratio, I'm not sure if it has LSD but it spun both wheels the other day in the wet.
There are a few diffs on gumtree at the moment as well.