The new machines are easy to spot. They have a big Silver Strike sign on top.I havn't been there in the last few months but I'll try to answer some of your questions.
Mirage - do all 5 machines have the same Centennial Sign strike?
No...Not when I was there....The one on the right of the two on the wall had the sign.The ones on the posts down the main walkway had danny in them.
Palms - do both machines have the same Halloween strikes?
They had the same strikes in July but I don't know now.
Slots of Fun - what strikes are in the machines?
One had leftover dam strikes the other had the "Wonders" Strikes and both had the Strikers RedCap.
Stardust - so all machines have the same strikes?
They did.
Plaza - where are the machines located and what stikes are in them?
Between the Blackjack tables and the main cashers booth. They had the Islands in one and the monument ones in the other. Redcap and signs in both.
New York - where are the machines located and what stikes are in them?
Westward Ho - where are the machines located and what stikes are in them?
?? I don't know.
El Cortez - where are the machines located and what stikes are in them?
Single line just above the stairs to the back room with "Wonders Strikes" and Strikers Redcap. Three line on the North wall with "monuments" and Preserving RedCap.
Las Vegas Club - where are the machines located and what stikes are in them?
To the left of the cashers cage down the hall. They had a lot of the leftover heads in when I was there and a few new ones Sign, strikers redcap, and one other I didn't get yet.