odyssey blocks are k24s, but they did put a k20 head on it (k series frank for the best of both worlds). As you said there was no cutting involved, maybe a dry sump was involved which means the bottom of the sump is higher than usual in which they can lower it more? mind you it did have ITBs so that increased its height but i dunno
not sure if the hight was so much the issue, but the Yellow k20a Jazz that is seen on the forums now and then has had the firewall cut (or so I've been told).
i asked SU-WOOP about it and he said that the place that did it would not give up the secret as to why and where the incision is made.
depends what you put with it, it may or may not need cutting. all i know is J's racing didnt cut anything (according to what they say)
by looking at this i dont think any cutting is necessary http://fitswap.com/install.htm#