1971 Plymouth Scamp ECS fuel tank vent

First have you made certain "it is" evap controlled? Do you have the extra vent line(s) coming out of the tank and (there may be) the separator can in the trunk? This system changed year to year, and I'm not sure ALL 71's had it. May have been a mid-year change.

So go back to the trunk, look and wrap your hand around the filler neck in the trunk, and see if there's a 1/4" vent tube going down the outside of the neck. If so you already have the older vent

If not, there's a couple of ways to deal with that depending on your creativity

LEAVE the 1/4" line going up into the engine bay, that IS THE VENT. Keep that line "high" in the engine bay to avoid siphon problems. Some guys advocate splicing that line into the filter bonnet or the valve cover breather (multi nipple) to help keep gas smell down

EDIT.............I did not see your second photo at first..........you could just branch the 1/4 tube coming forward from the tank into that breather