Question about the Ecu's. Got a 98 V70R ecu sittin in my garage & am wondering if it will fit into my 96 855 turbo? Is it a simple plug & play sawp or am I askin for problems?

 

Don't do it. I don't recall what the issues that others have ran into but you can do some searching on Volvospeed.com to find out what exactly what the issues are.
The '98 V70R is running an M4.4 ECU while the 850's use an M4.3 ECU.

The best thing you can do is contact Lucky at Ardideas.com. He can wright you an M4.4 conversion for the 850. I have his Blue Tune with an M4.4 conversion on my 850R and it's a very solid tune!