Some thoughts.....You didn't mention if you will be disassembling the engine?

There is at least 1 short hose that is difficult to change....I would change them all....but that 1 hose would be a "must do".....

Renew Belts....

Check chain tensioner on timing chain and oil pump....

Take FI Pump to Calibration Shop, as well as the Injectors

Install Exhaust Gas Pyrometer.....

Install Turbo Boost Gage.....

Renew Motor and Tranny Mounts....

Clean, Clean, Clean......

Look over Transmission cooler hoses.....

Inspect frame and body that was hidden by engine.....

Renew Flex Discs in Driveshaft.....since it's out anyway....

Address any Transmission issues that you may have.....

Check brushes on Starter.....do Insulation Resistance test.....

shoot....there is all sortsa stuff that comes to mind.....put engine in a good engine stand.....pop oil pan, examine crankcase, main and journal bearings, clean out any sludge.....

SB

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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG