Gas Cap Question?

['68OrangeSunshine]

It's always possible after only 40-something years of human intervention that a fuel tank could be swapped. I know I changed out my '68 OEM tank for a '67 tank from a junkyard, after a hot-tanking and a silver spraycan paintjob and new lmc float/pickup, in 1997. Two reasons: 1] then-new ethanol gas was dissolving some bottom sediments that had built up over almost 30 years; and 2] I had buggered up the slots on the fill neck when I lost the key to a locking gas cap and had to get it off with brute force. No design change between '67 and '68. Only drawback was that the gas gauge has never read right since. "Full" is at 3 O'Clock, 1/2 Tank is at old ''3/4 full'' indicated. I've never ran it out of gas so I don't know where the bottom is. Probably around 1/4 to 1/3rd full. I know how it reads, so I know the status of my fuel level, but a new driver [in the extremely unlikely event I ever parted with my rig] might be misled.
Does your tank have the second evaporator line out of the filler neck, like a '72? Does the Gas Gauge read screwy?
I'll go outside [in 101* sun] and pull the Stant p/n off my gas cap.