Dual Tank Venting

[learyw]

I have a 78 K20 with a 350 and dual fuel tanks. My fuel senders have three outlets. The fuel line, return line, and vent line. Both vents were plugged when I bought the truck. Clearly, this causes problems when the tanks heat up creating a build-up of vapor. It shoots out when I open the gas cap. Whenever I am at the junkyard I look at other trucks hoping to find a vapor canister or get an idea for how to vent mine. A few thoughts:
1. Every truck I look at that is similar to mine is different. Different dual tank fuel selector, a different way of running lines. Clearly, people change this system a lot.
2. What is the best way to vent mine? LMC sells a vent line for 2wd (part 32-3654). Not sure if that works on my 4wd. It doesn't look like mine every had a line. I would be surprised if someone went through the effort to remove it. Maybe. I could run that to a canister and then to my carb. I would also need to buy an aftermarket canister. Several hundred dollars in parts for all that...
3. What is the cheapest/easiest way to safely run mine? Plug the vent lines and buy a venting gas cap? I read a few people ran the vent line directly into the carb.
4. I have looked at a lot of vacuum line diagrams. There is even a diagram for my year and engine that shows no vent lines at all. How did they vent? Is this why some only have two outlets on the sending unit?

I have read every post I can find, but Im kind of lost on this one. Thanks! -Will