I don't think Ford made 9" rear axles in 85. Your F150 has either an 8.8 or a dana. both have a bolted on rear cover. I would suggest that rather than changing the gears in your axle, you get an axle from a junk yard F150. Then you can Bolt it in with no need for doing the close tolerance work needed to replace your ring & pinon.
Being that it is a 3.08 gear it is almost certainly an 8.8" rear.
Ford discontinued the 9" rear in 1987. It was in the trucks until the early 80's, but I'm not sure when the change was made, but knowing Ford they use the 9" until they ran out of the correct width and then changed over.