Need help with rim choices

[GMC69]

I've had my 1970 C20 for about 5 years now. I replaced the tires a few years ago with some Falken Ziex ST-Z04 in 245-75-16. I find that I don't get enough traction in the rear, not only in wet but also in dry. I drive it pretty normal, but once and a while do take off a bit quick.
I run 30psi in the tires.
I was thinking of going to a wider tire, but can't find what I want in a 16" to go on the rims I have already. I would like to run a 285 which would give me about 2" more in the rear, so about 11" tire.
My options are to go to an 18" rim for a tire that will match the height of my current tire and I can get the 285 width I want.

The problem is I can't decide which of the 2 rims to go with but also if I should stagger the rims. So keep a 16" up front and get the 18" for the rear. I would then only need to buy 2 rear tires. Or get 18" all around and buy 4 new tires. I barely have any mileage on the current tires.

Seeing that my truck has the black modding on it, I figured it would look good with a black with machined lip rim, but also found the same rim in just polished aluminum.

Which rim should I put on, and should I go 16/18 combo or 18" all around?

Below are the pictures of the 2 rims I would like to choose from and a couple shots of my truck. It's also on bags so one picture is fully aired up and fully down.

Truck


Up and down shot


Both rims