I have sold about 15 toploaders.
First, read what the other person said. There are MANY things that can be wrong, and all cost a lot of money.
Second, there were over 130 different toploaders. Some will interchange, most won't. For example, if it is a 5 bolt, narrow face, run away. Good for concours, but not much else. Person local has (had) one for sale for years in the $150, couldn't move it.
Could be close or wide ratio, big in vs little in, big out vs little out, BB vs Small Block, close medium or long shift pattern, and toss in a couple different tail shaft lengths, and the mess begins. Unless you know exactly what you are looking at, then you will wind up with someone else's problem child. Even the tag is no guarantee, as the guts, inputs, tails, etc. may have been changed out.
Then, after all that, when you find the killer deal for a great toploader for $600 and take it home, and REALLY look at, you will find you actually wound up with a SROD, worth $20/ton.
Buy the correct V8 T5 instead and be much happier.