318 cam shaft selection/upgrade for stock engine

None of the listed cams will come close to 18 inches of vacuum.

You are looking at a cam with duration at .050" lift in the 190' to low 200's range, and with an LSA of 112 or even 114. The specs above keep the overlap down, which keeps the vacuum up.
Racer Brown EH-4
Crane H248-2
Or maybe a step up from these 2 at the MOST like the Crane 693902 or Comp XE CL20-220-3 in the Summit catalog.

No knarly idle with these cams.

FYI, I have run a cam like the first 2 above and had 19-20"of vacuum.