The M104 is in my 97 SL320 and 97 C280 so I should remember how this is built up. Do the injector rail bolts go into the plastic manifold or aluminum? If aluminum then 25 nm / 18 ft-lb should be fine. If steel inserts embedded into plastic, I'd go 12 nm / 9 FT-lb. Pretty much a bit past heavy screwdriver tight so the insert isn't damaged.

Are you chasing a problem by changing the injectors? Be aware that ignition coils / wires / boots fail on this engine and will cause a miss fire. When this occurs, the computer will shut off the injector to the offending cylinder after 5 or so seconds so raw fuel does not melt the catalyst.

The 97 M104 in an SL or C is unique in that it was the first and last year for a M 2.0 / M 2.1 engine computer, electronic shift trans , metal key with an RFID chip. The M104 did continue in the S320 until 99.