I'm not sure what could be a square plate with 4 bolts in a close square pattern. There is nothing that needs to be removed in order to drop the crossmember other than the 4 bolts, 2 on each side.
I'm going to give you a step by step as if I were doing the job from start to finish. The pics that I posted show all locations of all 4 crossmember bolts and supporting locations. I also stated earlier and in one of the photos that I posted that you may NOT need to actually drop the crossmember down to access the bushings that you are replacing. I've never actually just replaced bushings so I'm not 100% sure but it appears that there is in fact enough room in there to remove all 4 rack and pinion mounting bolts and move the rack and pinion up enough to access the bushings for replacement. It's up to you to try this "Shortcut" to see if it works for you. Otherwise, follow the following instructions to lower the crossmember to replace the bushings.
1 - Raise the vehicle using a floor jack placing the jack in the location shown in the pics. Be sure to Chock both rear wheels to keep the vehicle from rolling. Raise it high enough to crawl under comfortably and safely.
2 - Place jack stands under left and right side unibody frame rails as shown in pics. Lower vehicle to have jackstands support the vehicle.
3 - Place the floor jack rearwards of the lifting location to the rear of the front crossmember and sway bar location and support the crossmember lightly.
4 - Remove all 4 crossmember supporting bolts using an 18mm socket and ratchet, universal wobble extension and socket extensions may be required to access all 4 mounting bolts.
5 - Lower front crossmember slightly leaving enough room to access the rack and pinion mounting bolts, these should be 15mm hex bolts. 15mm socket and extensions and or wrenches required for removal of rack mounting bolts. (keep in mind that since the steering shaft is still hooked up, the crossmember may not drop down very far especially on the driver side)
6 - Remove all 4 rack and pinion mounting bolts (15mm)
7 - Lower crossmember a bit more and just enough to access the mounting brackets for the rack and pinion and to replace the bushings.
8 - Replace the rack bushings, reassemble the brackets.
9 - Raise the Crossmember back up high enough to reinstall the rack and pinion mounting bolts and torque securely.
10 - Raise the crossmember back into place, install all 4 mounting bolts and install loosely.
11 - once all 4 bolts are back in place torque all 4 bolts securely.
12 - Position the floor jack back to the lifting position and raise vehicle off the jack stands.
13 - Remove jack stands and lower vehicle.
Keep in mind that a front end alignment is recommended any time suspension is apart to make sure you have no issues with irregular tire wear...
Keep me posted and let me know if you have any additional questions...