I have the 275/65/20 Ultra terrains on a 2019 Silverado with a front level only. They fit great and do not rub at all and I have 10000 on them so far and they are wearing great.
I believe they already have a 1.25 block stock, so this 2.25 block from readylift.com will give you the 1" you are looking for.
2.25" REAR BLOCK KIT - GM SILVERADO & SIERRA 6-LUG 1999-2020
$149.95
SKU
66-3002
4" lift should be enough for the 35" tire, you will probably need spacers for the 12.5 width to avoid rubbing the upper control arms. I am not speaking from experience just everything I have read on here.
I did a readylift leveling kit and am running 275/65/r20 (34.1x10.8) and have no rubbing at all.