In the near future I plan on doing an engine swap in my 300TDi D1. The original motor has just ticked over 485,000kms. It has been down on power for a little while, the timing belt is due soon as well as a few other minor things. I have a good spare that had the timing belt done, new vac pump, serpentine, new head, etc. so my thoughts are it is easier to just swap the motors out.
This leads me to my question, with the auto exposed, what preventative/service maintenance can happen (beside the obvious full flush) without the motor in the way.

TIA