I bought a used filter off ebay that was for a 5.0 engine he said, and tried to install it and it is slightly too wide and about 2 inches shorter than the fram paper filter I have. It will not fit well in the air box. Are the 5.0 air boxes different than the 4.9 air boxes that I have?

 

Yes, if you check you should see that it is two different part numbers for each engine. Cut your loses and go get a filter to fit your truck.