'67 GTX, vent lines?

[hemi68charger]

Hey gang...
I"m not too familiar with the '67 model year, but did the '67 GTX have a return vent line line those in '68 and later? The reason I ask is a friend is having problems with keeping his GTX running.. It'll run down the road for about 15 to 20 minutes, and then starts running really erratic. It's almost like it's vapor locking. He had a rubber fuel line from the pump to the carb, but I replaced that with an extra OEM steel line like it's supposed to have. He states the Edelbrock 725 he's got on it is good. If the fuel pump is bad, would it be bad all the time or is it a possible situation where it pumps, the pressure builds up in the tank (because there's no vent line or cap - GTX's have the flip-top design like a Charger) and then, after the pressure builds up, the pump can't deliver adequate fuel pressure? Looking at the sending unit in the car, it doesn't have a second nipple, just one for fuel delivery..