I discovered this the other day. Some kind soul has made available the Japanese assembly and service manuals for the Kawasaki Ha40 in-line engine, on this linked page:
http://www.aero.or.jp/isan/archive/h...0_and_ha60.htm
I downloaded the files (6 in total) without difficulty but as expected, it's in period Japanese script (very similar to classical Chinese script). Unfortunately, I am fluent in neither. So short of picking up 1 word in 20, it sheds no further light to my query. (Though I am in awe of the laborious, hand written nature of the technical translation.)
Perhaps someone with a working knowledge of the DB601 might be able to spot any obvious differences between the two engines from the drawings or technical charts?
...geoff
**Forgot to note reference page from J-aircraft website which sent me to the page with the Ha40 manuals.
http://www.j-aircraft.org/smf/index.php?topic=17127.0