Will a 10" wide wheel with 5.5" backspacing fit on the front of a third-gen or would you need to go 5.7" or 6"?

6" backspacing for sure. Maybe even 6.25".
And you can always add a shim but you can't remove material.

Shoot I was afraid of that. I'm going to see if I can shave off 1/2 inch of the back pad and bring the wheel in with negative camber around 1/4 at the top. I found a set of wheels with the 5.5 backspacing. Trying to figure out how to make them fit.

Have these wheels already been machined for the lug nut taper? Once that is done that wheel is what it is because you can't remove material from under the taper or it will weaken the wheel.

If you have the skills to do all that then you have the skills to measure out your wheel well and get this right.