Sort of. If you have stock springs now, the lift springs will likely be a little longer, which affects the placement of the axles a little bit. Likewise, the shackle angle can change, which affects the spring travel (you may want this, to run a longer shackle). Also, the pinion/caster angles will be a little bit different in this scenario. As you're choosing shocks, the best way is to cycle the suspension through full travel and the original spring won't give you the same information. Ultimately, a lot of people just buy shocks a couple inches longer and call it good, but it's best to know that you won't bottom out a shock, the front driveshaft, etc.
Putting 2" lift blocks at each corner is probably a little more accurate for mock-up than picking the frame up 2 inches and letting the suspension droop, as long as you won't drive it on the street in that form, but would probably cost you an extra set of U-bolts, etc.