1. The searchlights on the outboard side of the funnel were one level higher on Lexington.
2. Saratoga had a catwalk on the inboard side of the stack, Lexington did not.
3. The DF station under the forward 8" control station was faceted on the Lexington, square with an extension on the inboard side on Sara.
4. Minor differences in the bulwarks on the bridges - photos needed to sort them all out.
As for the Meng (which I don't have), if the description is accurate, note the following.
1. The stack gallery and .50 cal platforms below the 4 corners of the flightdeck were added in late '35.
2. The flightdeck was widened forward in early '36.
3. The 1.1" tubs and splinter screens were not added until late 1940 to early 1941.