Redhat Enterprise 7.3 configure Thin Client on Portserver TS16

I am migrating from SCO OSR6 to Redhat Enterprise 7.3, and that migration includes integrating more than 20 Digi Portserver TS16’s.

I was able get the 1.9-37 drivers provided by support installed, and it appears to be operational on the Redhat install. However, now that there is no functioning /etc/inittab any longer on RHEL, I am unclear how to configure the serial terminals.

I have read this page:
I am assuming that i will use /etc/default/grub to define the terminals instead of /etc/inittab, but there is still a lot of ambiguity (especially for configuring dozens of thin clients).

Could someone who has gotten this to work successfully give me a nudge in the right direction? Thank you very much in advance.