Lowering question for 72' SWB Fleet

[KrazyKevin]

I'm still very new to the 67-72' scene. Learning everyday. But, I've seen many pics in the forums with trucks from all ride heights and tire sizes. A 3/5 on one truck doesn't even come close to looking the same on another.

What I'm wanting to know: Can I run 18's or 20's? If so, all I want to do is fill up my wheel well. I just want a level truck. I don't want tires inside the wheel well where I can't see the tops of the tires. So, if I run the 18's or 20's, will I still need to lower? Or will the tire size take care of what I need? If I do need to lower, what amount?

Thanks

Kevin