Recently bought some 35x12.50x18 toyo open country mts and a 4 inch rough country suspension lift. They rub slightly and was trying to gather input on wheel spacers.

 

The "largest" spacer that can be used is ¼" (be sure it's hub centric) because anything more will not leave enough stud threads to secure the wheel(s).

To use a ½"+ spacer ...

1. you would need to replace all of the studs with 2"+ versions.
   .
2. the spacer would need to be hub centric.

The thinnest wheel adapter that you can go with is 1½" (because of the length of the studs), UNLESS the mounting flange of the rims have recesses between the lug holes to accept a portion of the stud, in which case you could use 1". Either needs to be hub centric.
.