At the time we had a similar integration, we were using the JDBC Adapter to connect to an AS/400. But there was a bug with the JDBC Stored Procedure Call Operation. So instead, we configured a Scripted Operation with a custom step. In the custom step, we used java code to call the SP.
Unfortunately, I don’t have a copy of the actual SP. But if you want to know more about the java calls we used, let me know.