Re” I did it. Everything went very well, but the two thunderbolt plugs are not working after all. LAn and USb is doing well. Any suggestions about it?” You need to disassemble the iMac again to the point where the logic board is loose (step 58-59 on this guide). Connect a thunderbolt cable, a USB cable and and ethernet cable to the back of the iMac with the logic board in place but the logic board screws not tightened. This will ensure the ports are correctly lined. Tighten the logic board screws and finish the reassembly (at this point you can disconnect the cables.) . This should solve the problem.

The antenna plate assembly is a tongue and groove type. The plate has a "groove" and the rim of the outer case is the "lip". You have to slide it in and align the parts ant it fits perfectly .