I have a 64 nova wagon, and I mounted my fuel cell just below the cargo floor in roughly the same location as the stock tank. I enclosed the cell in a sheetmetal box, and used a Moroso fuel door
http://store.summitracing.com/partde...part=MOR-85700
to access the cap. It passes tech this way at our local track, and is installed per nhra rulebook. I made sure to select a cell that wasn't too tall so it wouldn't contact the track before the rear bumper in case of an unexpectedly high wheelstand. My car is not a NHRA "class" car, but I would think this method would be OK for one as well.
Scott