You only need to remove two. Just loosen the othertwo where you see the slotand it'll slide right off.
If you have the tank and the horn off it should be pretty simple.
Get yourself an appropriate size allen wrench and cut a piece of it off ~ about 1/2" long. Then use a box end wrench to turn it.... Don't fret.... EVERYONE that does this, experiences the same "challenge"....
I did mine without removing the TB. Buy an offset ratcheting 1/4" wrench. Then buy an allen insert and use that to loosen and remove the screws. Just take your time reinstalling as the seals can be tricky.