First I would find out why the other donor withdrew his collection. Probably nothing there but his reason might have some bearing on what you are willing to do.
Second, if it is a loan, make up an accurate inventory (use a digital camera to photograph as much as possible) and have the museum sign off on what you are loaning.
Third, if it's a loan, there are no tax advantages. If it is a gift however, and you think it has substantial value, have a CPA help you with the tax aspects.
Good luck and it sounds like you might have a lot of fun with it.
Charley