Driveshaft length. Is there a solid answer?

You can certainly measure and have a new one made and it will be upwards of $450 in our area.But if you find that your combination is the same length as a 68 satellite or barracuda or whatever then a decent used one can be an economical choice.
Mine was a free..it came with some other parts i bought and needed but used ones around here can be $75 - $100