Can someone help me date these Eames chairs?  

hi thejoyfulfox,
The H bases of these chairs were produced starting in 1957 onward. So that SHOULD be an obvious evidence of the date. But the light shell also looks like it may have been produced earlier than 1957, in spite of the base it is on.
It is quite possible that they matched up some older "left over stock" shells with newer bases at the factory.
The fact that the light shell has no markings means there is a good chance that it's earlier than 1957. And if the underside of the seat is consistently curved near the rear mounts, and shows no additional flat spots (flat spots were later added to accommodate wide- mount bases) then you may even have an earlier- as early as 1954 - Venice studio first year shell. It is hard to tell from the photo, but it looks like that might be the case.
However, it seems a bit of a stretch to find a 1954 first year Venice side shell on a base that was not introduced until 1957.
If the shell does have flat spots next to the rear mounts, I would say that its probably a 1956-57 shell.
As for the green one, I'm less sure about it. I'm a little fuzzy about the embossed letters. Same base though, so probably 1957 or later.
Hope this helps.

That does help - thank you! 🙂 I actually meant to mention the flat spots, but I didn't. Neither one of the chairs has the extra flat spots for the wide mounts.

It is interesting to me that the early (possibly 1954) shell is on a 1957 or later base. That might normally suggest that old stock was around for up to three years before being used…
But now that widespread mid-century collecting has been going on for well over a generation, there is more and more chance of re-pairings and "wrong" pairings made by collectors before re selling items again.
The shock mount imprints are of course the best way to tell if a shell was always paired with a base.
As a generation of collecting and re-selling converges with the unique changeability of the Eames shells and bases, it is getting much harder to assume that ANY pairings are original.
But these particular mount impressions do look to be original to these bases- and the time lapse between manufacture of the shell and base on this chair may be the longest I have seen for an H-base chair.
The shell could possibly be a little later than 1954 also. Even if someone knows precisely when the stacking shell flat spots were introduced, that would not preclude the possibility that the earlier type shell could have still been produced for a good while longer.
If that is the case, I suppose this pairing could also be looked at as "proof" that the early style shells with no flat spots were produced all the way into 1957. All they would need is two presses operating simultaneously
I'm sure there was a whole thread on this on DA way back somewhere.