I was worried about getting the screws mixed up, so I used Sharpies to color-code each screw before I removed it (red, orange, or yellow - corresponding to the iFixit illustrations) When I marked the screw, the bracket got some color on it too, so when I was replacing the screw, I was confident that I was putting the right screw into the right position.
I also made a template-board by tracing an outline of the phone in the center of a piece of cardboard, and then gluing pieces of masking tape onto the cardboard, sticky-side up, one piece of tape for each bracket I removed. I drew an outline of the part on the tape, and made a red or orange or yellow dot for each screw that came from the bracket. It made it super-easy to keep track of the disassembly and reassembly. Took a little longer, but I didn't damage the logic board by using the wrong screw, and I was relaxed throughout the repair.
GPS and WiFi now work perfectly!!!
Thank you iFixit and commentators