Hello Thierry (and fellow modelers),
I would like to address the issues you have raised about the kit inaccuracies.
I am currently working on a replacement canopy for the Su-27 kit. It will include a vac canopy and resin detail parts to replace the IRST housing and lots of detial on the canopy framing and details under the rear coaming. My references are scale dwgs from the Polygon publications "Cy-27" and studying lots of photos. I have been posting pictures of my in-progress work here:
Trumpeter 1/32 Su-27 ..., How long have we wait...
starting on page 2 of the posting.
As for the intakes. Yes, they have lots of problems, one that you missed would be the fact that they are warped and bowed in. I ended up dunking them in boiling water to straighten them up. The missiles under the pylons nearly drag the ground on the model, which after checking dwgs, I concluded the same thing as you, the intakes are the wrong shape. This led me to studying the missiles more carefully.
After studying photos, I concluded that the scale dwgs I had seen might not be correct. So I searched the internet and kept finding the same answers in text. Alamo A has a fin-span of 77cm. In 1/32 scale that's 24.06mm, the kit measures 38.6mm. About 160% what it should be!
I posted some pics of how I am dealing with the missiles here:
Su-27 missile fix
As for the Black Box cockpit, it blows away what comes with the kit. Modifying the front coaming was pretty easy. Most of the modification will be hidden by the canopy framing. I posted a picture of the modified part here:
Black box Su-27 cockpit, does it fit ?
Despite the problems with the kit, it does have alot going for it and builds up into an impressive model. It's unfortunate though (especially since the kit costs so much) that us picky modelmakers have to deal with these problems and inaccuracies.