Very sound advice. 930s are some of the most difficult cars to get right, but when they're right, they're OH. SO. RIGHT.First, don't buy any 930 without an thorough PPI by a mechanic that has excellent and specific 930 experience. These are not "really" just 911s mit turbochargers. These have numerous and complicated sub systems that have to be functioning correctly or you end up spending more like Ferrari money for upkeep and repair. Don't for a minute think you are going to own and use one of these for SC/Carrera money. If you do, that will only be because you are neglecting it and sooner or later the bills will come due. A good many of them have needs either via neglect or run hard, etc. You can see and drive one that has broken rings, etc and it will run reasonably fine. I have owned several and all but one had needs. Only one of them had superficially obvious issues, but all were $$$ to get right.
Nothing wrong with modded 930s. In fact, most 930 enthusiasts consider them as simply the base platform for building a great performance car. Ruf did nice work but it is now old technology and the components are aging with intense heat cycles on them. A GOOD modded 930 is a better car. However I am talking about cars to use and drive, not collectors cars.
Also, have you driven these cars? A stock USA 930 is needy. Soft cam timing and compression..and tuning.. , wide gearing, heavy clutches etc..make them ... well, the choice is having a "collector" car that basically sits in the garage to be adored or having an enthusiast 930 that is fantastic to drive. The Ruf has the much needed 5 speed, should also have the superior Ruf sport clutch setup, and hopefully a "Ruf" kit on the engine/chassis. There should be specific records verifying what was done to any "Ruf car" but Ruf does not send out built sheets. They do sometimes verify information but the seller should have specific documents. [Don't take the Ruf 5 speed kit lightly. It includes the transx, complete clutch/flywheel, and Ruf shifter. I spent well over $10k setting mine up and got a "deal" at the time. When I last checked just the transx cost $14,500.]
Be careful about emissions. In California they are a real PIA with emissions standards that are far stricter than the cars originally were required to pass. Here they are all assigned in the BAR "High Emitter" list and can only be tested by more strict standards. In other words, if you are in a state with strict emissions, don't accept a smog certificate as meaning you won't have issues when your turn for emissions testing comes. Insist on an independent tests so you know someone isn't doing things under the table. Ignoring this can become a nightmare.
Again, you cannot be too careful. There are a lot of modded 930s that were not done well, or poorly cared for. Find and drive a good one and you are spoiled for life.
Good Luck
JR