Yes, that's the AC condenser. you can replace the drier as well. If you don't get the exact sized O-rings, install the one's you already have. Remember to lubricate the O-rings before inserting it.
Remove the front grill, horns, drier, the center metal piece that holds the hood lock/latch, remove the aluminum AC lines going to the condenser.
Pull a vacuum for 30-40 minutes before charging with gas.
Try here:
Condenser Toyota 4Runner 02 01 00 99 98 97 96 2 7 3 4 A C AC Air ACC4744 | eBay