Sorry I have not posted sooner, I'm fighting a tooth ache and seem to be winning this time!
I'm thinking it's similar to that pic which I also have myself. That Ki-61 has the Ha-40 engine which is somewhat like the DB-601 in the Bf-109E.
The Ki-61-II Kai and Kai Ko use the Ha-140 engine which I believe is again somewhat larger and is roughly like the DB-605 used in the Bf-109G series on up.
Also, in the Model Art Profile series Kawasaki Ki61 HIEN book, there are several pics of a Ki-61-II Kai which is the "razorback" version of what I did in this that shows the top in my opinion more flatter than the pic you posted.
But I still believe I should broaden and do more the highlights in this area as I feel now it's looking too boxy.
Thanks for the help everyone and I'll post more once I get the time!
