Old LT77 gearbox, to buy or not to buy

I'm looking at an LT77 gearbox at the moment from a 1986/7 2.5 petrol non-runner. It's looking a bit rusty, I have to say, but I'm not buying it to put straight in, I want it so I can at least put in a new non-worn output shaft (the one that goes in to the transfer box) and then get it in to my 1988 2.5NA. At the moment, it's going very cheaply, although that might change. I don't mind spending a little bit of time reconditioning this gearbox, I was just wondering whether I would be ****ing money away by looking at this particular one. I'd like to get my teeth in to it as a project, and don't mind it taking some time (unless the box in my truck suddenly stops making that awful clunk, and suddenly stops driving!). I'd just like to know if there are any pitfalls/money pits I should be aware of?

Here's some pics of the box: