With a torsion bar lift, you lift it until you reach the height you want. It's not a magical 2" lift.
Shackles for the rear are a hard number. The only thing to prevent the rear from increasing height based on what the manufacturer says (they offer different heights) is how sagged out your springs have become. For instance, if your springs are really week, you may gain about 1.75" of lift on 2" shackles. Just because springs are weak, not because shackles are faulty.
2" taller in the rear, and cranking the front so much to get level, the tires will probably look at tad small.
When I picked up my 2008 Z85 4x4, I torsion bar lifted the front to match stock height. That was about all I think it takes to make it still look okay.
Also, something to be aware of is using stock torsion keys to raise the front so much to mach the 2" rear left may not be achievable. The torsion bars sag over time, so your truck may be settled now. Lets just say it has sagged an inch. So as you lift the truck, the first inch of adjustment just gets you back to stock, but you've used a lot of the adjustment just to get there.
It's worth a try, but may not be something accomplished with stock keys on an older vehicle with so much height requested.
Be aware that that is about a full torsion bar lift. That means the differential needs to be lowered. Ball joints may need to be flipped (depends on the vehicle). And the worst of all, the ride quality goes to crap. Several have eventually installed a lift kit because the ride is horrible with tall torsion bar lifts. I'm in that boat, the truck rides very stiff.
Also, my Z85 has 1.5" rear lift shackles, and the front is almost level and I am maxed out...I can't lift enough up front to match a 2" rear shackle....suspension limitations.
And lastly, if you start tweaking the front end height you're affecting the alignment. So testing here and there keeps on screwing up your alignment. Don't do this work, or test, unless you're ready to start and finish then shortly after follow up with an alignment.
Some of the cons I've mentioned have been covered several times so I won't be writing it out again. Such as ball joints and differential lowering.