First find a trustworthy person who knows the RS inside and out. As has been said, some people try to build a fake car, and that is not what you want. Ownership history is a plus.
LSD is a bonus, but not a deal breaker. If it is a must for you, then you can have one installed later.
I am assuming you are in the states. There is no problem bringing cars into the U.S that are over 25 years old.
Being patient is your best asset. The no stories car, with full documentation are the cars that sell for the top of the market. Zero history, funny looking restamped VIN numbers or engine numbers are the bottom of the market.