The Spectra tank with internal baffling works great. Just order it without the filler neck.
The aftermarket filler neck (on Spectre tanks) does not vent correctly and the GN version does NOT fit a G body Cutlass correctly, not sure about a Malibu. You can read about it on multiple forums including this one if you do a search. The filler neck sits too high in the license plate opening. I cut an old OEM filler neck out and JB welded it in like the factory did originally. It fits like it should with no vent issues and looks great.
The procedure for installing the OEM neck is simple. Just cut the old neck out with a tin snips keeping 1" away from the neck itself. The old tank flange will peel away (with patience) and minimal grinding if any is required to fee the neck from the old tank. Once you have it separated, an undamaged OEM filler neck slides into the new tank like glove. Just make sure you apply enough JB weld to prevent leaks. Yes, JB Weld. It is 100% resistant to gasoline and GM used a similar epoxy in production. OEM filler necks are not welded.