I took a 4R70W from a 2003 F-150 and slapped it into a 1999 E-150. When I plugged in the driveshaft, the transmission was too long. There are two different length tailshafts for the 4R70W. The newer transmission in the older van is the shorter one. I swapped tailshaft housings (added the longer housing) and everything matches up. The problem is that the tailshaft is about two inches shorter, however, it is engaged with the driveshaft. Am I going to have any troubles running this transmission?

 

There is a very good chance that the driveshaft is going to fall out of the trans at some point. You need to change the output shaft, too. That involves a complete teardown of the transmission.