And what about fuel sending units? are the stockers being used?
Do you mean fuel LEVEL sending units? If you're switching to a fuel cell, I really doubt that the factory unit will work out for you. Level sending units are specific to the dimension of your tank/cell, specifically the depth. Most fuel cells don't have provision for gauges. You top em off and hope like hell you don't run out during the race. You calculate your pits ahead of the race to coincide with your expected distance between needing fuel, or whatever you might need replenishing. It's usually fuel dependant #1, then tires, fluids, etc. The thing is during a race, even if your gauge says you're low, if you got no pit comin up, you outta luck... On a short course, there are no pit stops, so you buy a tank capacity and fill your fuel no more than what you think you need. Again if your have a gauge that says you're low, it might as well read 'Outta Luck' as much as 'Fuel Level'.
That said, if you're setting up a fuel cell for recreational use, you really do want a fuel leve gauge. For the sender, be sure you get a capacitance style sender and not a float style. The abuse of off-road can really play havoc with float style senders, and you'll end up having to re-calibrate all the time.