http://hasport.com/store/index.php/accessories/wiring/ecuadapters/obd2a-2b.html
need the ob2a to obd2b adapter. the above link will take you to hasport who sells them
If you want to use ebay stuff that is fine. Its your car not ours, but when something happens with it(and it will) every will tell you "i told you so". So by all means if you want to use stuff from ebay by all means do it.
Yes, you could weld this but from experience it will do it again. Might as well get a decent header now instead of having to deal with it cracking again at another time
http://www.jspecauto.com/page.aspx?page_id=17#3
scroll down and find 96-00 Honda Civic Engine Swap Matrix this will tell you what you need to do a 2000 civic si to put a gsr in it