I am getting ready to put in the fuel lines and am wondering what dictated two (fuel/return?) vs. one in 1967. Anyone know this?

Bill

I think any car with a 4 barrel Q-Jet. L34/L35.
Holleys 4 barrels only had a feed. L78/COPO

Ddual fuel lines are a 69 and later feature. Every 67 and 68 Camaro has a single fuel line, either 3/8" (V8) or 5/16" (L6, maybe 327's as well).