Timbo,
What do you want? A roll cage generally implies a 6 point cage that includes A pillar bars. A roll bar generally implies a four point cage ( so a hoop behind the seats and two diagonal bars down towards the rear corners of the load area.
Basically, any cage that fits in a soft top will fit in a hard top. A four point cage should go in just fine. A 6 point cage won't go into a hardtop without cutting and welding the cage into position.
Bear in mind though that generally, a 6 point cage that fits inside the cab will make you car LESS SAFE IN AN ACCIDENT.
That's why they are hard to make legal. It's because you will loose headroom inside the car and the likelyhood is you will hit the cage with your head in an accident.
6 point cages really require race seats, harnesses and helmets to prevent you from getting killed by hitting the cage in a crash.
Just a thought.
Obviously, an internal cage won't do anything to save your car in a roll - it's only there to save you.... which is pretty silly if you've been injured by striking the cage with your head.
My preference is for an external cage for the front two points. The rear four points can be done internally by passing though the roof.
Like this (obviously this is a ute, but it's relevant for the front bars):
Not only does an external cage make the car no less safe like an internal cage, it will save the car in a rollover.
Another option is to weld a kind of exo cage into the body. I have done this with my ute
You can see the front pillar here:
and the rear pillars ( in progress) here
This setup has saved my car from quite a few flops and an onto-the-roof roll.
there's another option:
"Roof sliders"
This car still has a six point cage, but there are no longitudinal bars above the doors inside the car.
Just some ideas. Sierras are terribly hard to put a roll cage in and keep the car safe.
Steve.