Hate to do this... 20" wheel question

[randomhero472]

I know.. i know, another f'n wheel question, and i really hate to do this but i FINALLY found the perfect wheels for my project, but am slightly confused of what some of this means, and want to be 120% sure these will fit before i order. Specs of the truck will be bolt-in bag setup, bolt in c-notch, and i'll be keeping the stock inner fenders, and keeping the stock bed tubs.
Now for the wheel specs:
front will be 20x8.5" and wheels come in different configurartions
What is the "offset" these wheels are offered in either 15mm or 40mm offset, what exactly is this? Backspacing offered is either 5.3" or 6.3"

Now for the rear.. wheels will be 22x9.5" and are offered in 15mm or 42mm, backspacing 5.3" or 6.4"

SO... WHAT WILL FIT AND WORK BEST??

I've searched for over an hour, and i am sorry to post up one of these threads.. just looking for info , thanks guys!!

EDIT: dont know if this matters or not, but it also lists "hub bore" as 72.6