Hey Ray, ...Manilla Brown is the correct color that Ford designated. I have the formula for PPG's DCC Concept line however they have discontinued this paint. FWIW, I am SO upset with PPG that I have changed paint brands totally. Currently I am testing Axalta's Matrix and their Imron lines and both look very promising (-unlike their Chroma lines)
Ken Ehrenhoffer and I have been trading/collecting formulas however my suggestion is for you to determine which brand & line of paint you want to use first. Then have your jobber contact their HQ and see if they have an older formula for Manilla Brown that they can cross. If not, you will need to use the latest version of the Paint & Refinish Book and have the color scanned to determine the formula in the line you want to use.