i have [in the pics that follow] a tank that i'm not certain what year z it fits. the one on the left in the first pic is the original tank from my 73 240z. in the middle is the unknown [i'll call it "x"] and the right is from an early 280 [or so i was told]. the 280 tank i just removed from my 73, i had installed it a few years ago as i read it would be great for a track car as it had additional baffling [compared to a 240 tank]. i have now replaced it with a modified 240 tank with an internal cell and additional baffling. here are some measurements and other info.
length; 240 & x are 35", 280 is 38". distance between the tank strap indentations are; 240 & x are 15.75", 280 is 17". fuel feed/return diameters; 240-8mm/4mm, x-8mm/8mm, 280 i don't know as it was modified with an -6 fittings [feed where the drain plug was and return in the orig location]. vents; 240 & x have 3 total-at the end and 2 at the top, 280 has 2 total but at the top.
you'll also see some other differences. the 280 tank has a raised area just under the spare tire well. it has the fuel feed/return toward the middle and below the tank seam [where top & bottom halves join] and is indented in that spot, 240 & x tanks have them adjacent the sending unit in the top portion above the seam. there is another difference, along the right side[near fuel filler at top] you'll notice the beveled edge that nestles along the subframe [that sub provides support for the bumper mount] curves the same for x and 280 and differs for the 240.
so, i hope someone can help me to id the 'x' tank [i suspect 74] and perhaps nail down the applicable years for the 280 tank [i believe it is for 75-76] but may be later. ok, here are the pics...