Gas tank removal?

[Slofarmtruck]

I will be installing a new gas tank on my 86 C10 long bed truck this coming weekend and am looking for some advice on the best route to take. My biggest challenge is the plastic cover that surrounds the current gas tank. Does this cover just unbolt? I currently have a 3 line sending unit and since I removed my emmissions components on my truck do I need to order another 3 line unit or will the 2 line unit work? or am I not thinking this 3 line 2 line thing properly. I hope this all makes sense. I just figured the 3 line was a supply, return and vent for emmissions, and the 2 line was a supply and return. Any help is greatly appreciated!