If you find a donor truck, its an easy switch. You can do it without a donor, but would have to get the right length driveshafts made up.
The NP203 transfer case gets a lot of bad press, but its really not a bad case. Its heavy, but durable, and the full-time 4WD is very convenient if you want 4WD but may be going on and off hard surfaces. If yours has been rebuilt already, that's even better.
For a swap you would need the 4wd version of the 700r4, and if you find one in a GM truck it will probably be mated to an NP208 already. Its probably just easier to buy the combo and install it together. Getting the right driveshafts is relatively easy, since that combo was used in early to mid eighties Blazers. Any decent driveshaft shop should be able to make them for you, or you may be able to buy them off the shelf.
You don't need the lockout hubs right away, but without them you will always be turning over the front axle, even in 2WD. You don't need a carb adjustment, but you need to add a TV cable for the 700R4, and some way to run the lockup torque converter. There are add-on kits from several sources.
Do you know what axle ratio your Blazer has? On pickups the 700r4 is nice because many have the 4.10 axle, but some Blazers have more in the range of 3.00-3.23 ratio.