I prefer the Spectra tank which allows use of a factory pump hanger. Part# GM307C includes the filler neck
but it will not vent properly. Get part # GM3C which comes without. Cut out your factory filler neck and JB Weld it into the Spectra tank. It will fit perfectly and also fixes the alignment issue caused by installing a Regal tank into other Gbody cars.
Depending on what LS engine you have you may or may not need a return line. If you have a newer LS engine without a return line on the rail you can use a Corvette C5 filter / regulator. Mount it close to the tank and run one line up to the engine bay. You can do your own shopping but most of the best prices I find on E bay.
I mounted my C5 filter / regulator behind the Vin 9 exhaust heat shield. Just like GM would have done it.
IF you require the return line, then you could use a 4.3 EFI Monte Carlo filter and mount location by the passenger side lower control arm mount.
http://www.ebay.com/itm/Fuel-Tank-S...ash=item1a0d89e50a:g:a6oAAOSwvUlWs-cq&vxp=mtr
http://www.ebay.com/itm/Fuel-Filter...ash=item4d49cbf8f7:g:DbMAAOSw8d9UyWnG&vxp=mtr