The MUSTANG script ones can usually be cleaned/polished with a little chrome polish.
The others aren't worth messing. Ford parts will fit and appear best, so if your budget allows, look for the quarter ornaments, hood letters and 289 emblems. The early small pin running horse NOS emblems are very rare and expensive these days. Any that you might see for sale with C5ZZ numbers on the box could be the later '68 style, which has large pins and I believe 1 or 2 of the pins in a different location. Good repro may be best, although I'd clean up and repaint any originals with good chrome and no broken pins.