Front driveshaft question

[379redneck]

I put a 6inch lift on my 87 and took the driveshaft to get it lengthened because it wouldnt reach, or so I thought. The guy measured it and the distance from the tcase to the diff and said he doesnt understand why it wont reach. He told me it will and he took off the dust cap(I didnt know it moved and thats what was holding it back) and it reaches, but not like he said. He told me it would be just at the end of the splines, but it would be ok. So I went to put it on and the splines are sticking out about an inch and I can barely get the cap back on. Do I need to get it lengthened or is it ok with the splines out that much? I just dont like that its maxed out against the dust cap when the truck is on the ground.
Thanks