I have collected several ECU computers from 850 T-5R, 850 R, X70 T5 manual, etc. These are believed to be working, most were removed from running vehicles, a couple from the salvage yard. These ECU's rarely go bad.
If you have an 850 turbo and want to add power, you can purchase a R ECU and add performance, a R or T5 ECU will give you more performance over a GLT programmed ECU.
Interesting fact, the 1998 T5 and 1998 R ECU's are programmed at the same boost level and carry the same performance. So, there is no reason to get a R ECU over a T5 ECU when dealing with a 1998 x70 vehicle.
If you have any questions, feel free to call or text me. I also have a video on YouTube about the ECU's. "Search R ECU replacement for Volvo's Robert DIY"