Hi Bes,
Have you tried my version?
The project you linked has their specific gRPC service hard coded into the Gatling actions. It is unlikely that it can suit your need.
Giving credit where it is due, it helped a lot in understanding what I had to implement, when I tried to stress test my gRPC service with Gatling a year ago.
I know a blog post is no substitute for documentation, but that story I wrote a while ago may be of help to get you started.
Good luck with your test!
Regards,
George