Im new to optics so forgive the n00b question, but Im looking for help mounting a Vortex Viper PST on a one piece mount. It seems I need to mount the scope with 4" of eye relief, so Im looking for help as far as making sure its leveled and plumb

Thanks!

My preferred method of leveling my scopes is to put a feeler gauge between the flat portion under the turrets of the scope and the flat portion of your scope mount.

Spin the screws evenly so that the scope still turns in the mount but doesn't have any up down play.  Insert feelers into the gap until it's full, this will level the scope.  When it's full you shouldn't be able to rotate the scope.  Then tighten all your screws down and remove the feeler gauge. Once the feeler is removed torque to spec.

I use the arisaka scope leveling system,best 30.00. I ever spent google arisaka  engineering

Jaqufrost has a easy and excellent method,  however if you have a mount with too much of a gap such as the aero precision ultralight, then you will benefit from a plumb line and a leveled surface.

Tools: feeler gauges, wheeler fat wrench, badger ordnance "dead level", plumb line, flashlight, white wall, acetone and gun scrubber (for blind threaded holes in the mount).
Note. At this point (prior to fiddling with any of this), I have degreased the mounting surface of the scope,  the ID of the rings, and the mount screws, with acetone. Be careful with acetone. Do not get it on the optical surfaces.

I set my mount up on the dead level, zero it out, and place the optic in it. I then level the vertical crosshair with the plumb line by setting the scope to 1x or its lowest power, and shining the light through it to make the image of its reticle against my wall/the plumb line. Alternatively,  I will look through the optic with the plumb line just barely to the side of the vertical crosshair. This allows me to align it better, as the crosshair on some optics are thicker than the variance I'm willing to tolerate from true.

Obviously you have already set eye relief before doing this. I just wanted to restate.

I then place the front ring cap on the scope and tighten it with a torx bit and my index finger and thumb, once all is level. The goal is just to keep the scope from moving around, and with quality rings, 1 to 3 inch pounds is all you need here, for now.

I then place the rear ring cap on the scope.

Once the rear ring cap is all aligned fore and aft, I use feeler gauges to get the gap equal on both sides prior to inserting the screws. I then, if warranted by the manufacturer, will apply loctite to the screw threads. (I personally always do. Screw what the manufacturer says, it gets 222MS.) I then drop all 4 screws home, and finger tighten them and then recheck the gap of the rings on either side with feeler gauges to insure equal gaps. I also pop a look through the glass at my plumb line again.

I take my wheeler fat wrench and set the torque to the correct setting. For nightforce unimounts, it's 25 inch pounds. For leupold isms mounts, 25 to 28. For vortex, 15 to 18. For geissele super precision, 15 to 18, for badger ordnance, 15.

I then begin tightening each screw gently, a tiny bit at a time. I go closest to me right, furthest from me left, closest to me left, furthest from me right. In a cycle of 4 to 6 passes, I will have achieved correct torque and the wrench will click over. I then do one to two more complete passes. (Fun fact: most scope tubes will show about 20 thousandths compression, 10 thou on each ring gap. Although this is not accounting for any deformation of the ring, jjsy results from feeler gauging post torque. Just an observation of mine.)

At this point I again verify my deadevel device is zeroed out, and then revizualize the reticle and plum line to verify the scope did not shift. If it did, I immediately loosen the screws and fix things, then repeat. If it has not,  I repeat the above process on the front ring starting with removing the thumb or barely tight screws.

Ymmv, and everyone has their own zen when it comes to putting their glass in a mount,  but this is mine.