I've got a few coolers knocking around and found if you remove the fan from a Spire cooler, you can run a 3000G passively (without a fan), however this may not be great for the vrm's etc with much lower airflow.
If you're happy to zip tie the fan on the outside then it does a great job, a case fan moves more air, quieter and does a slightly better job!
Next step will be to see if a Prism will fit (I think the fins will be in the right orientation to encourage indictive airflow so may work passively quite well?),
still may have issues with other components overheating.
Also a 240mm AIO to try, although this will likely look ridiculous, should be fine without fans (on a 3000G), might be able to fit a case fan on the inside of the case as well to promote airflow in the case.
It is worth noting that the 4650G is all round a much more powerful CPU and also far more likely to undervolt well which means you can lower your thermals whilst still getting better performance than you would with the 3400G but compatibility is in question here...