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This may be a dumb question, but what is with all the back and forth behind the tank with the fuel breather line? I pulled my tank a few weeks ago and was surprised at the length.

Not sure, don't recall that. Hose goes from tank to fuel separater (on left, ignore wasp nest) then to hard line that goes up to charcoal cannister.

Very neighbourly of you, giving those wasps a place to build a home like that.

Perhaps I have misunderstood the connections. My tank had no hoses attached when I took it out. I will look more closely at my running car. I assumed the breather line was the longer one. If not the breather line, then why does the fuel supply line go back and forth on the bulkhead behind the seats?

On many emissions control spec cars the breather hose takes a serpentine route to the carbon canister, the idea is that if the fuel tank is overfilled the serpentine section of the breather being mounted above the tank level prevents raw fuel getting to the carbon canister, the various bends help trap any fuel vapour that might condense in the line.
At least that's the theory behind it, as to it doing anything useful in the real world is entirely another matter!

It's a long time since I mucked with this stuff, but my recollection was the breather came off the filler neck, not the tank, then to the vapour separator, then to the carbon canister.

I don't recall having to touch it to R & R the tank.

Hasbeen

The breather comes from inside the tank (small tube inside the tank):



And exits by the filler hose:



The hard pipe(s), the supply side goes to RH side:



Vapour line seen here (also fuel return line for FI set up). It does meander a bit on the rear bulkhead, probably to prevent condensate from reaching charcoal cannister as previously mentioned:

Thanks. My '79 DHC doesn't have a charcoal canister. So the fuel supply line follows the right side of the car and the breather follows the trans tunnel, which is what I assumed. I just didn't know that the meandering of the breather was to allow for condensate, etc. Thanks.

What are you going to do with the engine bay side of the "breather" pipe? You can't cap it as the N/A version is a sealed system and a vacuum will develop starving the engine. If you leave it open gas fumes will exit into the engine bay area (not much but would make me nervous). You could plumb it to the intake but you'd have to be careful with vacuum. Normally it is under a slight vacuum as determined by intake manifold/carbs/cannister reducer etc. but not so much that it overpowers the pump. Not sure how to figure out the best configuration. You could cap it and use an English gas cap (vented) but a friend that used an English locking cap said he could smell fumes.