Automatic to 4-Speed swap

im going to be in the process of tracking down parts soon myself. but if your gonna do the swap, might as well get a 5 speed.

The short tail shaft Toploader that came in those Stangs is a direct swap for a C4 dimensionally.
They use the same mounts and driveshaft.

The big thing that needs taken care of, other than the obvious clutch pedals/linkage, is the speedo cable.
The cable for the Toploader is longer and the gear teeth are helixed in the opposite direction.

I don't know exactly about your Stang, but I converted a Maverick... all that needed done was to drop the steering column and install a complete set of pedals. I dropped the steering so the entire bracket could come out, and then put in the 'new' manual bracket with pedals already in it.
Then you need all the linkage/brackets in the engine bay.

If you go with a T5, then you can use the T5 bell and the stock clutch cable, rather than linkage. I believe the T5 needs a conversion (custom) crossmember to mount it. Also, the shaft may need modding.

Don't get a long shaft Toploader, they are meant to be a direct swap for a C6, and they never came in Stangs.
Also make sure to measure the input 'nose' length so you stay away from FE trannys. They are identical except for this crucial measurement.
If you decide to go with Toploader, go with wide ratio version.

I know nothing about a T10, other than it is not as strong as a Toploader.

where are you located?
I might be selling mine in the spring.