Don at FCFab has a VERY slick method for getting cages beyond a tight fit
He basically cuts tube sized holes in the floor. He then "drops" the cage through the floor so he can fully weld the cage up. He then jacks the cage up, cuts the tube, and then welds the cage feet plates in.
VERY bad description I know... but the point is he can get the cage within 1/2" to 1/4" of the roof
As I said, I don't know what type of clearance I have above the headliner. So right now, I'm just trying to see what I can do.