As I recall, with the spring and idler pulley out of the way the fan and water pump pulley don’t have to come off. The tensioner arm will pivot enough to make the damper lower bolt accessible. The OE idler pulley bolt takes a 5- or 6mm hex bit. I only have those two sizes and I’ve never had a problem.

If it hasn’t been said, the fan clutch is held by a regular right hand thread bolt. Hopefully the 603.970 water pump has the tall ridge like the .971 water pump that lets you slip a holding pin into the backside of the water pump pulley. The .96 water pump has less of a ridge that won’t hold a pin. Or use a tool that holds the rim of the pulley. There’s a MB special tool that easy to fabricate. It’s a pity HF stopped selling this but it should be available elsewhere -



Spend some time with an M103 belt tensioner before you call the 603 tensioner the worst.

Sixto
98 E320s sedan and wagon
02 C320 wagon