Dlasure2

I think the big boy brackets would be the ticket. for the price it cannot hurt. I could cut the roof off, then I would look like one of those dogs you see with it's head sticking out the sun roof

RWKHausSupply

I am 6'5", 290lbs. I built a Stock class XJ for Ultra4 (King of the Hammers) 2 yrs ago. One stickler was NO body floor manipulation or holes etc. I am in No way a fan of the exo cage, especially for a Stock class rig, and wanted a full internal. This couldnt be just some basic small tube cage either, it had to pass a tech inspection with mandatory helmet to tube clearance etc.

Given I have no head liner...

I was able to research and find a set of very high quality seats that are suspension style and race quality that allowed me to sit lower in the frame then the other brands.
http://corbeau.com/products/fixed_back_seats/baja_xp/

Those sit about 2" or more lower in the frame then the PRP mastercraft beard etc. And they are more comfortable as well as the shoulder slots for belts are still acceptable height for tech with my 6'5" frame sitting in a seat.

I dont know if those seats would help you in your situation though. As I had to build a seat cage tied to the main cage to mount these to and my seat brackets were all custom. But I will say they look like they would be the same height bracket mounting points as stock, just moved a bit back also. When sitting in my seat with a helmet one (thats about 3" larger OD then my head) I have over 3" to the roof (remember no headliner). I did remove 1" of seat bottom padding from the 3"+ that they come with. It was a easy mod since the seat bottom is a velcro in place piece with velcro'd material around the foam.

I have sat in many of stock XJs with PRP's or Mastercrafts, and my head is ON the headliner the whole time and I cant even sit up straight. I would NEVER own a XJ like that.

Attached is a picture from a little while ago, but the seat mounts are kinda seen. And they dont look any lower then stock, maybe the rear ones a bit...