Look at tag on driver's door, last line has 'axle', underneath is the code.I don't know how to post links , but here is address for Ford axle codes :
I know axle code links appear time to time on the '99 and up board, but I don't have that info.
Yes, like Jim said , the tag on one of the bolts on the housing, to decipher the code on the tag, (again forgive me , I canot post links) go to Carpentractors page, here's the long way:
Go to forums page, go to top of page and choose from the menu bar 'faqs',On next page, click on '94-97 Power Stroke FAQ',on next page,go down list and click on 'Links', Of member web sites, choose 'Carpentractor', on his page choose 'Identify your differential'.
It breaks the groups of numbers on the tag down for you, also gives a look at the Dana bolt pattern, just in case you have one .
I might mention , on my tag , the first 1 or 2 digits is covered up by the dam bolt.
I have a F350 dually stroke with a '45' axle code on the door , so my axle is a non limited slip Sterling (Ford) , ratio 4.10. I have chalk marked the drive shaft and spun the jacked-up wheels and verified 4.1 shaft revs. per one wheel rev.By the way, if both wheels spin when you turn one wheel, I (think) that means you have limited slip, but someone more knowlegeable needs to confirm that.
Someone can correct me , but I think if your axle code on the door begins with a letter, then you have limited slip, but if it begins with a number , then you have non-limited slip.
Of course, if your differential has been changed out, the door code may not help you.
Tom , '96 pSD cc dually, 158k.