I did mine so long ago I'm trying to remember all the details.
From what I remember, the stock tubes are really in the way.
On my truck I removed the heater core and flipped it over. Then I drilled two new holes in the firewall above the gas pedal that lined up with the two copper tubes. Then I cut the tubes shorter with a tubing cutter so that only 1 1/2" was sticking into the engine compartment. On mine I slid two hoses on the tubes and ran them along the top of the motor to the intake/water pump where they connect to the engine.
You can kinda see how they end up in this picture.
Like I said, it's been a long time so I don't remember every detail. I think you may have to tweak the copper tubes a little too but I don't remember exactly how much or why.
Mine is a '76 so I don't know if they are all like this and it's been a while since I've seen one at a wrecking yard.
I'm sure there will be other people along that can clarify this or provide a better solution.