I recently found a 84 Volvo 760 diesel that I'm going to look at tomorrow. It looks like we are in the same boat!
www.volvoforums.org they know there stuff
from what i gather they have a oil starvation problem but the fix for that is fill it a qt over full and it wont have any problems
right now im in the process of replacing the injection pump belt and going to time the pump because the pump belt broke and it is being a real pain stripped out a bolt and got it out this evening
but now to get the belt on and get the correct tension on the belt i have to loosen the pump bracket mounted to the engine block and i cant get 2
bolts lossend up so tomrrow ive got re think my plan and get some more tools over to my house from work
if you need and help feel free to ask im in the process of learning but i might be able to help you out
the engine is made by volkswagon