The “injector relay above the radiator” is a 7/9-series thing. On an 850 the relevant piece is relay #103 in the main fuse/relay box. It can fail on the ECU/injector side while the pump still runs, so “I hear the pump” doesn’t clear it. Do this when it won’t restart (takes 10 minutes): Spark vs fuel...

You’re seeing a few different fasteners get conflated. On the 850 timing setup there are three distinct things: Hydraulic tensioner body bolts (2x): these fasten the hydraulic unit to the block. They’re M8×1.25 and the torque is 25 N·m (18 ft-lb), then +30° per Volvo. The later/wide-belt lever/stack...

Short version: yes, aside from the later-style parts, the only hardware you need to add is two M8×1.25×~40 mm flange bolts for the hydraulic tensioner body (Volvo 988179). The T45 pivot bolt for the tensioner roller is plug-and-play, no custom M10 needed. For best belt tracking, also use the later i...