I think the Ford recommended drain/refill or manual transmissions is 100,000 miles.
That said, I changed the fluid in mine at 9000 miles and noticed a lot of initial break-in wear particles (it looked fairly metallic).
The AMSOIL website is a great tool. Even if you don't buy AMSOIL products, their on-line ordering can tell you capacities for the various cars systems.
I out the AMSOIL full synthetic ATF in my GT's manual transmission. It uses he same fluid as the v6 manual trans
2006 Legend Lime Mustang GT/Manual Trans
/some mods(tired of updating) 13.257 @ 109.36 on stock 18 fanblades and stock BGFs wth CAI, tune, UDPs
1967 Lime Gold Galaxie 500 XL/390 4bbl/Toploader
1966 Mustang Coupe/bare metal (rebuild in process-slowly)/engine&trans