I just did a in cab replacement on my 72. From what I learned (or think I learned lol) during the process, there are three types of original tanks.
67-69 non-EEC
70-71 with EEC and
72 with EEC. The 72 had a smaller ID fill neck and cap.
EEC systems require the non vented cap and non EEC systems require the vented style.
Appears most all replacement tanks with EEC are based on the 71 design. Which has the larger ID fill neck and cap. I did not find an exact replacement 72. I used the 70-71 style EEC tank.
As far as the sending units and small blocks go.. I read that in 72 the return line was introduced on automatic trucks to help with vapor lock. These are the sending units that have two lines on them along with the three line fuel pump. 67-71 have the single line 5/16 sending units; 72 manuals had single line 3/8 and 72 auto had dual line with 3/8 supply.
This pic shows a tank with EEC. Note the vent lines.
