ah no, you do not need anything from the REAPER SDK since the only file you need (reaper_plugin.h) is included in the SWS source tree, with permission. It's also newer than the SDK one.
I've updated some outdated stuff in my above post, just updated the wiki too, and its URL BTW (we've moved to github in the meantime...)
=>
https://github.com/Jeff0S/sws/wiki/B...-SWS-Extension