Most common is to add a "roof bar" which either runs front to back at the center of the windshield bar and main hoop that bends up to touch the roof. Or the same idea but diagonal.
I could see what you've proposed working, but it needs to be blessed. Email HQ and get their input since they are the ones that make the final call.
Thanks, I'll go ahead and email HQ with the idea and see what they think... We've thought about the front-to-back centered bar, but because the current cage is damn near right up against the roof, we didn't think it'd buy us much unless we drilled through the roof anyway... which we don't mind, but seems like an awful bit of trouble considering the car is a T-Top and right/left main bars are exposed already.
I have seen this done but the bars went from the header bar back to the main hoop. We are in the same boat as you because we have drivers ranging from 5'7" to 6'4". Our solution is to raise the mounting point of the slider off the floor with a 1" x 2" tube welded to a 1/8" steel plate we are putting down on the floor pan and then the back of the sliders are on the floor. That gives us about 2" +/- of height difference with the seat all the way forward to all the way back. Plus, out tallest driver will take the padding out of the bottom of the seat to give him a little more clearance from the bar. BTW, we are not doing an exo cage. Hope this helps
This does help, I think that may be how we end up mounting our seat's sliders regardless of how we get more clearance out of the cage.
Solution #1: Do a bent center bar that joins header bar and main hoop. It's ok to have one with a kink in the middle or on the ends. It won't be much but it'll give you an inch or so of extra clearance, which might be all you need.
Yeah we don't need much, we're just looking for a few good inches to help out with visibility and with the taller drivers. I forgot to mention the visibility issue we've got right now with the car. Other than the tallest guy, everyone else has to sit on cushions/tarp/phone-books to get their eyes over the dashboard enough to see.
Solution #2: cut out the floor from rocker to trans tunnel and from rear footwell to pedal box bend (not sure if fuel/brake lines go there, so be careful with that). Cut off the reinforcement that runs down the middle, weld a 2x1" steel square tubing perimeter (like this stuff , re-weld it. If there are fuel/brake lines, make sure to make an indent in the floor for them to keep them outside but inside the floor plane (shallow c-channel should work), and keep them covered with a welding blanket while you work. Weld strips of 1/8 steel as reinforcements for your seat mounts.
This is something I don't think I even considered for our car. "Can't raise the roof? Drop the floor." I think it would hurt our visibility too much right now since we can barely see over the dashboard. Shame, really, because that sounds like a real badass way to fix this problem.