The truck five speed is completely different than a car trans. The Z trans was the same length though, and it will bolt in. Also, the B210 had an A series engine and the trans would bolt on to the engine but would be tilted over too far, the L series engines lean to one side. I had a 78 620 with a L20B and a five speed. It had one working brake and many big dents and rust. I got it for $35 at a city impound auction and later cut the roof of and made it into a convertible. Never had any problems with it and it had a lot of hard miles. Engine ran perfect and the trans was tight.
A grand is kind of high, you can get decent ones for less than that, but if it is in real good shape and its worth it to you, go for it. Check out
WWW.NWDE.ORG, they have a lot of good info on their site and a great forum(a bit small but theres decent traffic).