Driveshaft Mistery???

I bought a 67 Barracuda with many extra parts. The Barracuda supposedly had a 318 engine originally with an automatic tranny. The car came with a driveshaft (laying on the floorboards). The car came with no engine or tranny when I bought it (8 1/4 rear). This drive shaft has a larger trans yoke (it won't fit into my 904). It has a 3 1/4 diameter and is about 45 1/2 inches long (center to center). According to charts that other members have posted (yes, I did some research) it could be a 70-71 Challenger (45.6 length), or a '71 Challenger (45.79 length) or a '70 Challenger (45.85 length). The chart I found at FABO lists three different part numbers for the different lengths. My question is, "where is this P/N found on the driveshaft so I can determine what it fits???" I want to sell the driveshaft but don't know how to advertise it. From the chart it seems as if it would fit '70 thru '71 Challenger with 340, 383 or 440. The lengths are so close it really shouldn't make a difference...RIGHT?????

thanks in advance,
Treblig