Nah, you don't need to. Two tough parts about the timing belt change on the 850 are:

1. Serpentine belt tensionser
2. Getting the old belt off the crank damper

Regarding the first... my father's 95 GLT has the tensioner with a square recess that is too deep for my regular rachet to fit in (rachet fit in my 92 960 perfectly). Volvo has a tool for this, but I eventually put a small piece of an iron strip diagonally in the square recess, and turned it by gripping the iron strip with a large vise-grip. There's not much clearance between the tensioner and the strut tower, so getting a tool in there is a big difficult.

Getting the belt off the damper was difficult because there is a small tab by the bottom of the damper that leaves just enough clearance for the thickness of the belt. You have to twist the belt so that it fits through that small gap, and then pull it clear. Installation was no problem though. Another way is to remove the damper, but I didn't want to risk rotating the crank and messing up the timing.

Total time to replace the 850 belt was about 1-1/2 hour. The 960 took 30 minutes, mainly because neither of these problems are present on the RWD.

The belt itself is ~$35 from FCPGroton, and a new serpentine belt was ~$22... get a large C-clamp (6") for $10 to compress the hydraulic tensioner, and maybe $20 for a set of jack stands, and you're good to go.