LastCo was not using a source, it was a binary server.
Binary servers are not really popular in this forum due to them being illegal, also discussion on them is allowed, but posting them is actually against the rules.
There is no source that is actually based between there, but Arco upgraded Hybrid's 5017 basic source to 5018+ which will match the encryptions used around that patch (Blowfish) and only packets would need to be updated.
Otherwise there is the CoEmuV2 source or whatever the name was which is based on patch 5095, so you could always downgrade that.
Although judging by your post I'd assume you have no knowledge about anything related to programming nor even the surface of programming for Conquer.