Kind of after the fact now but curious what I should have done. Responses may help others. My 77 tanks have three outlets. When I dropped the tanks one was plugged, one is main gas and one was vented with a differential vent.

The tanks has worked well for years with that configuration so I just cleaned it up and put on a new vent.
Montana does not have emissions testing requirements so that is probably why the previous owner stripped all of that off.
The truck is back together but when I was doing some work under the truck I could smell the gas fumes venting. Not real concerned about it because in 15 years of driving I never noticed fumes or had any issues but is there a better way to vent these tanks?