Does the em1 cmc fit directly in the 07 Si? I've read about people replacing them I'm just not sure how much work is involved and if I have to modify anything.

 

It's not directly fit, you must take push rod from your cmc and replace at 6th. gen. civic cmc.
Take look at this http://www.hybrid-racing.com/tech/ho...o-06-civic-si/ and yes, you can buy other cmc from 6th gen. civic and put in your car and pipe line can bi banded but be careful . have luck