I have the same Vortex level on my scope and I leveled the recticle using a plumb line. I put a level on the Picatinny rail to level the rifle (even if the stock isn't perfect, the rail will be level), then leveled the reticle in the rings with the plumb line, and finished by leveling the bubble mounted on the scope tube. I have a swiveling bipod with a lock and peripheral vision allows me to see the level while the rifle is shouldered. I level it and then lock the bipod down.
And recently acquired stock I stripped, sanded, and freshly painted: