quick backspacing question

[SGJ72]

thinking about putting some 15x8 Rallys on my 72, but these wheels have a 4.5" backspace. as I understand, that's so they can tuck under better, yes? so I can run a taller tire? I haven't lowered the truck any yet, and may not get to that for a while. so, running this backspace, it's not going to make the truck look weird, is it? like, too narrow a track? if so, I could run down some 15x8 Rallys with no backspace, probably.

I searched all through here for an answer to this, and probably read it sixteen times, but I wanted to be sure before I do it. thanks for any help.