In order to fix the problem with cooling... what about installing deeper annular radiators?
When you read about the problems with the DB606 they were a lot more than just not having enough cooling. The entire engine layout/installation was a mess., especially the oil system When the DB610s were fitted though it sounds like much was resolved.
I find this comment supposedly from Göring of interest though: "Why has this silly engine suddenly turned up, which is so idiotically welded together? They told me then,
there would be two engines connected behind each other, and suddenly there appears this misbegotten monster of welded-together engines one cannot get at!"