Should need two outlets I would think. One for fuel out and one for fuel vent. On the driver side versus passenger not sure why either. The capacity is 16gal for SWB and 20 for LWB "most of the time". I've heard that some trucks came with different gallon sizes on some trucks like 16 gal. on LWB but I think this may have been a special order or just the factory workers recovering from a hangover on the weekend and grabbed the wrong one
On the year I think they should be close until 87? when the wiring changed. This is also when the wiring for the valve from driver to passenger changed as well.