I may be missing something here, but I'll share a few thoughts...
[*]Most important thing to me is this question: "What degree of accuracy are you expecting at 1760yrds? Are you talking about sub-MOA? 1MOA? 4MOA? If you're happy to simply hit a pick-up truck at a mile, then you're not asking very much. Take out a half sheet (4ft x 4ft) of ply-wood, prop it up at 1mile, point your rifle way up in the air above it, and hit it. If you're wanting to hit a game-sized target at a mile, then things get a bit more interesting.[*]Here are a few "helpers" if you can't get enough elevation adjustment into your scope and bases: Mil-dot or other ranging reticles can give you 15-20MOA of "in view" elevation compensation. Putting an artificial aiming point at a known height above your target can also help you compensate for bullet drop - if I put a 2MOA circle (~30") on a 20ft post above a 4ft target, that's basically an extra 11MOA of elevation that I can compensate for. So if I put the bottom post of a mil-dot reticle (5mil = ~18MOA) on an aiming point 16ft above my target (11MOA hold over), that's 29MOA of free elevation adjustment before I even touch my scope or base.[*]Where you take your shot and on which day will make a lot of difference in how easy it is. You can't go shoot 1mile just anywhere, so as you're thinking about everything else in this equation, think about the range you'll use too. I have a few places where I can shoot up to 1600yrds, some are wide open looking down a gentle hill and I can shoot into or with the wind instead of across it, whereas other "ranges" I use are in a valley among hills where breaks in the hills around it make for switching or swirling wind conditions along the entire path. As expected, one of these choices is more frustrating than the others. So look at where you'll be shooting and how it could make your shot easier or more difficult.[*]If you rebarrel and restock your lightweight mountain 700, it won't be a lightweight mountain 700 any more, as it could be a heavy barreled rifle with a full BR stock. It also doesn't have to be a 300RUM any more, as you'll have the option of making it whatever you want that will fit the bolt face (or replace the bolt as well).[*]I'd be looking for the highest BC bullet I can get for this job. Velocity can't outrun aerodynamics, so find a bullet profile and weight that produces a high enough velocity to stabilize well, then produce a sustained super-sonic velocity across the entire range.[*]$1000 would not, in my mind, buy a proper RIG for this job. A proper scope, MAYBE, a proper rifle, MAYBE, but not a complete rifle & scope together.[*]I don't know Rubenator at all and I don't mean this to be offensive in the least, but when you're saying that 500yrds and more is new to you, I have to ask - when is someone going to start asking about the Indian, instead of just talking about the arrow? I've generally seen a breaking point where most shooters fall off after 300yrds, then another majority group falls off at 600yrds. 1760yrds is a long [beeep] ways, regardless of what rig you're shooting.[/list]
I'm certain you can get it done, these are just 'food for thought' items that come into my mind. I've done quite a bit of 500-800yrd shooting, enough 1,000yrd shooting to have realized I wasn't ever going to be competitive, and a bit of 1,200-1,600yrd "see if we can hit anything" fun shooting that I'd see this as a VERY daunting proposition, unless the accuracy requirement isn't very strict. I'd call 3MOA at 1760yrds a success for me, but maybe you're expecting better.