The easiest way to update the SDK is to copy over the headers from the Code::Blocks sources. Note that you need compatible link libraries for wxmsw26.dll and codeblocks.dll, too (matching the exact build that the plugin is to be used with). If you have compiled Code::Blocks yourself, just copy those files too (or set the linker's path). If you still use RC2, then you can download the matching SDK from codeblocks.org. If you use an unofficial build, then... I don't know -- if the build includes the libs, then all is fine, if it does not, then you have a problem.
However, working on the plugin now may not make an awful lot of sense, because your precious work will be worthless after the next release (which is finally being worked on).
I had stopped working on the plugin about 3 weeks before RC2 came out and (despite having planned otherwise) only taken up work again on Saturday.
In the mean time, a lot of significant things in Code::Blocks have changed, and cvs is no longer on the feature list, so an almost complete rewrite reusing some of the existing components seems easier than working on with the existing sources.
Apart from that, significant changes to UI, behaviour, and settings are being made (which are neither compatible with the old versions, nor with Urxae's modifications).