1974 Dodge Dart Sport "Hang 10"

H22A4 said
Does it have a 7 1/4 or 8 1/4?

8¼. Will know the final gear ratio when the mechanic gets to it.

H22A4 said
Looks like some of the interior Hang 10 bits are in decent shape (dash panels and seats)?

It doesn't look that good (the back seat has a moldy look) but I haven't cleaned the interior yet... so I don't know the extent of the damage.