I want to run my brake lines before I get my body on the frame and I need a new pinion seal so I have to figure out what I got.

I was sure it was an '86 F150 with 3:50 gearing but the seal I bought didn't fit so before I go and get mad at the parts guy I want to make sure. It has a bunch of numbers on the third member but I couldn't find any on the actual axle:

S318D

3 50 9 5A16

E3TWBA

3074

What the heck does it all mean?????

Sean