put the extensions on like ford84stepside said but put spacers under the front of the extension where it bolts to the front of the stock tracks. this will cause the bench to be lower the further back you put it.
I installed tempo seats with tempo brackets. I pretty much cut 2.5" off the brackets and they allow you to move the seat back all the way to the back. Like 1" off the rear bench I love the way I sit in the car now and I have a bunch of room between the headliner, granted I'm only 6'0". But these seats are so comfortable, they even feel better than my brother in laws E class Mercedes seats.
Yeah but I'm only 6'6", 275. LOL I have Fox-body buckets in mine. I just drilled new holes in the seat frames and moved them back on the rails a few inches. And they sit a little lower than the original bench seat.