A Ford rearend, or not?

An friend just brought a rearend tag to me and I said, Ford.
However I dont recognize the numbers on it.
Top row is, S3771S R
Bottom row is,
4L10 75 9B05
I thought Ford started with a "W"
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Well I found out its in a 99 ranger.
But what ratio?

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

this denotes a 4.10 locking ratio KB

--
ThunderSnake #9 Warn once, shoot twice
460 in the pkup, 460 on the stand for another pkup
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

S377 Is the plant code R Denotes interchangeability affected internally

Build year B Build month 05 Build day

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.