Reviving this old thread for people coming here from Google only to realize that the two log files in question no longer exist. It also makes me shudder when the default answer to the question is to run a bunch of windows commands meaning people are running their SCM server on a windows machine. *shudders* - there I go again.
Anyways, if you are looking for the server version these days go and find the plastic.relevant.log.txt which should be located in /opt/plasticscm5/server/ and open it up in your favorite editor like vim The top line should read something like:
2017-10-02 00:00:19,268 INFO ServerStats - PLASTIC SCM SERVER VERSION: 6.0.16.1408