[DeTomaso] Gas tank breather

[Brian Dudley]

I am slowly getting my car back together and I have a question about
the gas or fuel tank breather.
My car has a Motorcraft lockable gas cap which says it emissions
rated, I presume it is vented. My gas tank also has a Hall Pantera
rollover valve and a pipe running to under the car. This vent pipe
smells of gas, badly, gives me a headache when working in the garage
and I have inserted a plug which stops the smell.
Do all Pantera's smell of gas from the vent pipe?
Do I need the vent pipe if I have a vented gas cap?
Should my Pantera have a non-vented gas cap?
My car is a 1978 if that makes a difference.
Thank you
Brian.