I was able to get this worked out. With the very helpful instructions found here, RUT301 comm between PLC's in different subnets, this got me most of the way to a resolution.
In my scenario, I don’t have the ability to reconfigure the gateway. To overcome that, I had to set a basic NAT rule with the Action “Masquerade”.
This was a successful bench test based on a real world application, which I have yet to validate. I will provide an update if this does NOT resolve my issue.