The first part of this is not correct. 83s had 9" rears. They did not go to the 8.8 until 86...same body style, but with EFI (5.0) and 8.8s. But if it has a back cover on it, it is most likely an 8.8.Most 83's have the 8.8 not the nine. Look at the differential cover. If it faces the rear then it is a 8.8. If the Carrier bolts in the front then it is a 9.
incorrect...my 85 came factory 351w with the 9 inch....I would love to have a 9". That being said I have an 83 with a 351W and it has from the factory a 8.8". I do remember reading that Ford did have some 9" through the 83 model year but in 84 they all went to 8.8.
snap a pic....I am positive I have a 83. I am going to crawl under when I get home. Now you have me thinking I am crazy.