mount a cross bar between the frame rails and bring a radiused bar through the gas filler hole. If there isn't enough room for that I bet you can incorporate a cross bar behind the bumper and utilize the factory mounting holes.
Only problem I have is your car is a backhalf car and you where able to weld in that square tubing to the rear frame rails. My car is not tubed and I have all the stock stuff in the rear and I do not know if the stock rear frame will hold. I also cannot tie it in to the rear down bars on the rollcage because mines are welded close to the shock upper mounts.