The front suspension (except the hub in the spindle) and frame are the same between 2wd, 4wd, and awd.
The transmissions are different but you can swap a 2wd trans and tailshaft assembly for a 4wd assembly.
Within the same year group/trans type, any 4wd a340 transmission can take any other a340 transfer case. I am using a 4runner j shift case in my tundra now. Any 4wd 5 speed a750 transmission can take any a750 transfer case. There may be seal differences so please check before running anything. You can in theory mix transmissions and cases but it takes fab work.
The transmission crossmembers are different. But they swap with the 4 bolts closest to the frame and interchange. Use a tundra one to be sure, you will also need the 4wd transmission mount to go with it.
You will at a minimum need the front diff, it shouldn't really matter which one you use, first gen taco, first gen tundra, first gen sequoia, and 3rd gen 4 runner are all the same size/mount.
Since you are planning to run in AWD mode you could probably just lock the add system out or lock it in locked mode and call it good. I locked mine in lock since I am running manual hubs up front.
Make sure the gear ratio matches, probably also want to run an open front diff since the turning radius and steering effort are way higher with a locker up front on my truck.
In the rear, you will need a 4wd driveshaft as they are different.
Depending on how you go about actuating thr transfer case, the factory ecu never knows or cares there has been a change. If you have abs, the speed sensors are at the wheels, of you do not, you will need to extend the speedo sensor wires and make sure you have the sensor in the new transfer case. I used my 2wd sensor in the 4runner case and just added like 12" of wire.
Finally, you will need to either swap the wheel hubs in your front spindles for 4wd add hubs or find complete spindles from a 4wd add tundra or sequoia of your generation. These are different depending on year because the lower ball joints are different. 00-02 use the smaller ones and interchange with the taco and 4runner, 03-07 use the bigger lower ball joints.
I swapped my truck from 2wd to 4wd with manual hubs and manual transfer case a few years back with minimal issues other than the above.
Sean