Technotil I is an on row packer which l think might work on your drill or you could try to copy it.
See at technotil.com
See at technotil.com
That is one headache I have not solved yet and just removed the last attempt at a following harrow before drilling this spring, which used KV TS harrow tines and did very little. By far the best slot closure had been from a separate pass with a stubble rake, across the direction of drilling.