How to tell if Lightning nodes are lnd, c-lightning, eclair
As far as I know there is no way of knowing this on a protocol level... What you could do is to set up your own nodes (each node with a certain implementation) or some people say publicly which nodes they run. For example my node is c Lightning, ACINQ is using eclair and I believe rompert is running on lnd.
Also on 1ml.com some owners register their nodes and tell what they are running. Of course they could lie...