I figured everything out with my speedometer gear issue!
I pulled the existing gear out of my transmission today to really SEE what it looked like.
The manual transmission gears have a shorter shaft on them than the automatic transmission gears do and will not interchange. They might work the other way around, but not in my situation. Not a problem though!
I went to the Ford Dealership with my gear and showed them what I needed but with 18 and 19 teeth on them (I have 17 teeth on mine). They pulled out a sheet with gear teeth counts and part numbers on it and looked up the numbers to find out what stores had them in stock. I had to drive about five miles out to another dealership out in Nampa to get them, but I have two new gears now!
I purchased a 18-tooth gear and a 19-tooth gear, and I will see which one is most accurate.
18R gear - $4.40 - P/N CODD-17271-B
19R gear - $3.37 - P/N CODZ-17271-B
Might have some fun with the new axle starting Sunday!
Thanks for all your help guys, hope some of this info provides useful to current and future members!