I should have stated in the original post that the switches are EX4200 models.
I don't have the command 'request virtual-chassis routing-engine master switch' avilable to me, however there is 'request chassis routing-engine master switch'.
After some further reading, I came across this KB article (http://www.juniper.net/techpubs/en_US/junos15.1/topics/task/verification/virtual-chassis-ex4200-gres.html).
It looks like I will also need to enable Graceful Routing Engine switchover, which shows "off" when running 'show system switchover'. Then it says to run 'request chassis routing-engine master aquire'.
It looks like I could use either 'aquire' or 'switch', but is there any issue with running 'request chassis...' vs 'request virtual-chassis...'?