Could a Deacon Be Clerk of Council?

The Church Order specifically gives you the right, at the local level, to select whomever you wish as officers of the council, the consistory, and the diaconate (Article 36). Typically, these are officebearers. Selecting a deacon to be clerk of council is certainly possible. Most councils prefer to have the clerk serve for both council and consistory. That would make the selection of a deacon a bit more problematic since deacons don’t serve on the consistory. But it is entirely your prerogative. 

My other suggestion would be to indicate that it is also possible to appoint a capable person not serving in office to do the actual work of recording and correspondence under the guidance of the selected elder clerk. For example, I have seen retired persons who once served as elders now serve in this capacity with great joy and enthusiasm. You could ask such a person to make a “vow of confidentiality,” and use their time and energy to everyone’s benefit.