I bought this and put in storage, waiting for the rite project to come along. I really hate to sell it but need the funds to finish my current project.
I have one arneson/borg warner 1721 thrust tube only. I do not have the drop box or any additional parts. The thrust tube assembly is complete and in good shape, shaft spins freely and smooth. There is light surface rust on the input shaft. [ATTACH=CONFIG]542191[/ATTACH][ATTACH=CONFIG]542192[/ATTACH][ATTACH=CONFIG]542193[/ATTACH][ATTACH=CONFIG]542194[/ATTACH][ATTACH=CONFIG]542195[/ATTACH]

That's not a 1721 unit, rather it's for a 1720 inline

It was my understanding that the it having Borg warner casted into the side of it means it was 1721 and that the only differance between the two is u-joints

Oh no.. They are not interchangeable at all. For some reason someone designed the two differently. Yours has a Screw on ball, the 1721 has a bolt on ball, yours has a preload nut, the ball does this on the 1721, yours has a 1380 U.J, the 1721 has a 1350 U.J. your has a course spline U.J, the 1721 has a much finer spline, your as a 1 piece propeller shaft, the 1721 has a three piece shaft, yours has a seal block the 1721 does not.