Yup, set neck instead of the through neck. IIRC, they did a Firebird Studio as well as the Thunderbird, but with full size humbuckers instead of the standard Firebird's mini humbuckers.
I'd imagine that there's bugger all difference in the sound in the real world. You'd think the set neck might need to have a thicker body than the through neck, but it never really effected the SG other than the position of the neck pickup.
Another very short lived series.
Again, IIRC, it was linked to Dave Grohl (before he started using the Trini Lopez).