I have read some of the other posts about 390 casting #'s. I read that the one with a Z will work for a mustang. What about a "W"? Can truck bellhousings have the letters cast on them also?
There are two types that will work for you. One has a casting mark C60A from Mustangs, Fairlanes, and the other C5AA from 65 up Galaxies.
Image below is the C60A unit with accompanying engine plate and dust cover. The C5AA is basically the same with insignificant differences. It uses the same engine plate and dust cover. Except for the casting numbers which can be clearly seen, both look the same at first glance.
The only problem you'll run into are 68 up Mustangs had a different type attachment for the clutch fork so when you hunt for a fork you need to get one to match the bell housing you have.
The 390 pick up bell housing is easy to ID. It has raised ribs on the outside. It will not work for you.
I have a few of them but no pictures on file.
Let me know if I can help with more info or pics.. [email protected]