[Mart]

If this is out of Grandpa's car, it's important that you check the numbers on the trans. They might match the frame number and paperwork. If so this is the original trans to the vehicle and should stay with it.

If it is from that car I would not do anything with it until I have ascertained the viability of the rest of the vehicle. If you can see a way forward with the rest of the car re the bodywork, then the trans is probably one of the easier items to deal with.

Empty any water out. Fill it with oil and set it to one side in dry conditions until the whole vehicle -plan has been decided upon.

Being a 39 and a Merc, it should have the better synchros and shift tower.

Pull the top and take some photos of the insides. Let us have a look if you want some clued up advice rather than wild guesses based on assumptions.

Mart.