Throwout bearing slipped off clutch fork

Well, I've gotta ask- make sure you are using the correct throwout bearing. An 18 spline/hemi bearing will never work on a 23 spline input. I've actually seen this. (Hemi parts are heavier duty, right?)
More likely: with the scattershield, make sure you've got the right fork pivot. The wrong pivot will not locate the fork correctly. These pics from Brewer's, depending on which scattershield you have:
Brewer's Performance - Mopar A833 4-Speed Transmission and Component Specialists (brewersperformance.com)
Brewer's Performance - Mopar A833 4-Speed Transmission and Component Specialists (brewersperformance.com)
And check the fork length, like TMM said- Brewer's lists your application at 10 7/8" overall.
I feel for ya, it's hard to tell what kind of a hodgepodge of parts we get with these cars after 50 years.