What are the proper glides for Eames Zenith shell chairs?  

Boot glides
are probably correct.
You can buy replacement boot glides on ebay. (Just type in "Eames boot glides")
Make sure they are specifically intended for Eames x bases.
PS: Of course if the bottoms of the legs have holes in them, then it would indicate that "domes of silence" glides were used. But I doubt they are that old, as you say the shells are second generation.

Cool
thanks Eameshead!

Here are some photos
photos

These chairs are on eBay right now
Are you trying to sell em? If so you can get boot glides from Modern conscience or eBay but if you're getting em for yourself get them from Graham Mancha in the UK (google) as he uses OEM parts. I have bought a couple things from him and appreciate his communication and advice. I have the same chair (same color too) and that's where I got my boot glides.
http://www.mancha.demon.co.uk/spares.html

Hmm
Was not aware you could get "OEM" boot glides.

I think you are right woody...
It says right there on the Graham Mancha link: "please note, these glides have been made recently".
( It has gotten so bad that I now grow suspicious of any vintage item that arrives NOT wreaking of cigarette smoke. That is the true test.)

Oops
Only the shockmounts are OEM. What are the dates for dome of silence? I know plastic glides started in 1957. Trying to nail down the period when boot glides were in use on DCM, LCM, and x bases.

lots of overlapping dates
but if you generalize...
domes of silence: 1949 to 1952 or 53 ish
boot glides: 1952-53 ish to 1955-56 ish
These dates are for shell chairs/bases. I am less certain on when the specific dates for DCMs and LCMs. I would imagine they are similar though.