I've read a bunch and search a bunch, so if the answers are out there, I missed it, read it so long ago I've forgotten, and/or know it and just want to put in it one thread.

In my 1976 F150 Custom I have the 19 gallon gas tank. I want to put in a 38 gallon gas tank. The Spectra from JC Whitney has two categories: Without or With a rollover valve. The LMC 38 gallon has one With Evaporative Emissions Control and one without.

This leaves me with a few questions:

What is a rollover valve?
How do I know if need a tank with or without one?
How do I know if need a tank with or without evaporative emissions control?
Why do the two seemingly similar tanks have two different options?

I want to buy a bigger gas tank. Please help.

Thanks in advance.