Yup, the flat screws in the top pic are the ones for your synch tubes. Careful -- they're aluminum, and should not be snugged too tight. They tend to fall off the screwdriver and get lost, so try to find a screwdriver that fits the slot tightly and (carefully!) press it into the slot, so you can lift the screw out on the end of the driver when it comes loose.
Adjustments are made inside the carb. As Tews19 noted #2 is the fixed carb. The other three have a small locknut on a threaded shaft with a slot at the top. Remove the tops from 1, 3 & 4 to find it. Use a small wrench (8mm, I think) to hold the nut loose while you turn the shaft with a small flathead screwdriver. When the vacuum reading matches #2, hold the shaft with the screwdriver while you snug the locknut.
The knurled brass screws in the lower pic are the fuel/air ratio adjustments for idle. Close them, and then turn them out 1.5 turns. If the idle is rough, turn one in and out a half-turn, returning to 1.5 turns if there is no change. Try another one and listen for change. Keep going until you get some improvement. If nothing changes, start over at 1 turn out each and repeat the procedure, then 2 turns out. Somewhere in there is a sweet spot, and it took me a lot of trial and error to get there.