Buying an SVX, and I have some new questions

[CDG]

I have just come back from test driving another SVX, 1992, Purple, 170K kilometers. Body is in excellent condition, my #1 pick of the 3 I've looked at so far.
The other SVX is 1992, 150K kilometers, body is ok, and did have a $4k repair, mechanically feels and sounds good, but again the AC doesn't appear to be working.

Both vehicles are asking $10kCAN, I have been advised by a friend to offer $5kCAN and my 87 Accura Legend Coupe for a trade.

Issue#1:There is a grind, or binding when it is turned sharp at very low speed. This to me means that a limitted slip differential is not slipping, or is locked. The car drived quiet in a straight line.

Question#1: what is the construction of the driveline, is it an integrated front Diff w/limitted slip, a transfer case with/without limitted slip, and a rear Limitted slip Diff? Or could this be something else?
Question#2: how can I tell if its the front, rear or other?
Question#3: What would the cost be to replace a diff in the SVX, assuming I do the labour, if possible?

Issue#2: The air-conditioning compressor is most likely seized.
Question#4: is the AC compressor a standard off the shelf unit?
Question#5: What is the cost of a new and/or used compressor for the SVX?

Any help would be greatly appreciated.