General Fuel Tank Venting ?

This pertains to a conversion project I'm working on - putting a 6.5 na into my 80 Jeep CJ7, but is a general question about using an existing fuel (was gas) tank in a diesel swap.

I'm wanting to use my existing gas tank - it actually already has a return line plumbed in so that's good, but it also has 2 (vent) lines that ran to the charcoal canister (Evap system).

Should the vent lines be plugged, left open, or just leave hooked up to the charcoal canister? I know I either need to modify my existing gas cap to vent or get a venting cap.

Thanks in advance.

Joe.