Yeah, me too. But it made sense for our vehicles to do it this way until the better way came around.
They needed a charcoal canister to meet evaporative emissions standards (which is a good thing), but the canisters they had at the time were mounted pretty low on the frame rail.
This worked fine 90% of the time, but they knew these rigs were going to be used for all sorts of work and play activities. Some of which might put them on a nose-down or side-hill attitude for extended periods. I know mine got there a lot!
In those cases liquid gasoline could work it's way up to the charcoal media and ruin the function of the canister and add more fumage to the air. And gas to the ground too. Not good either way.
So the higher mounted tank allowed for two things. If the tilt caused fuel to flow up the vent lines, it got caught up in that tank. If it even made it that high.
And it could take enough vapor when conditions were right and just let the liquid condensate flow right back into the main rear gas tank. Hence the two lines to the rear tank and one only to the front.
So it did at least serve a purpose. Glad they came out with the better idea later though.
Mine took longer than most back then, but eventually started to leak out of the seam at the top and every time I filled the tank the cabin would fill with gas fumes. Lovely...
Got the new style on my '68, and one going on to the '71 next.
Paul