Having done both, here are my observations:

Engine mounts: vibration
Injectors: gentle rocking back and forth

How much blowby on this engine? My 603 has essentially none, so I assumed good compression and jumped straight to injectors.

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Garage:

2017 Chevy Colorado Diesel (nanny state emissions)
2005 Volvo S40 T5 AWD, 77k
1987 Mercedes-Benz 300D turbodiesel, 4 sp auto, 156k - 28.7 mpg
1996 Tracker 4x4, 2 door, 16v, 3 sp auto. 113k - 28.6 mpg

WARNING: this post may contain dangerous free thinking.