As the only Ar 234 bomber units known to have become operational were 6., 7., 8. and 9./KG 76 then the four machines you mention should have come from 7./KG 76. In that case their full codes would have been F1+BR etc.
Just one point: "Bombenwurf" was also the term used for bombing practice flights. If operational, the final column ("Bemerkungen") will usually describe the target and sometimes any defence encountered.
This book has an appendix listing all the KG 76 missions at the end of the war.