engine change help with BKP

[cfcorp]

Hi guys,
While driving to today my car lost all power, I pulled in after freewheeling a bit, I cranked the engine but nothing. Long story short the timing belt is loose, i think the stud for the tensioner broke as the belt doesnt seem broken, i d imagine the engine is kaput. I really need the car for a few more weeks, so I have a mate with a working 2.0tdi with 187k on it, condition unknown, I was wondering just to make it last would i be better
1. chancing the engine for the 2-4k miles i need it, afterwards ill probably scrap it and im going to get a new car on finance
2. replace the 77mm hex key on that engine, can you put the longer one in?
also might be a good idea to do the belt but im not sure its worth it, ill check if it was done.
Regarding the hex drive for the pump, is it a matter of just removing the sump to get at it, as i dont really want to strip it down too much as ill end up having to do the other stuff like belt etc.
im not sure what to do, but i really only need it for a few weeks 6 max, or 2-4k miles etc
thanks guys