Can't be done - not with your two restraints, CIS and 2.7 displacement (okay, maybe if you bolt a turbo on it).
You need to either increase displacement, or replace the CIS system. The cams that are used with CIS (not a high-performance system) are relatively mild. The 1973 911RS engine got about 210 HP (you can probably get more by bumping the compression higher than the stock 8.5:1) with Mechanical Fuel Injection, which has individual throttle boddies, and can run a hotter camshaft without affecting the fuel injection system.
This is all explained in my Engine Rebuild book (
http://www.101projects.com).
The 1974 911 & 911S engines used the older-style heat exchangers, which are nearly identical in design to the SSIs. As such, the 911S engine was rated at 175 HP min. I would suspect that a 2.7 CIS running SSIs would put out about 175.
Now, you can upgrade to some higher compression JE pistons, and run a 964 cam in your engine, but I doubt that you would get 210 out of it. See this tech article by Noah for more info:
http://www.pelicanparts.com/techarticles/911_engine_rebuild/911_engine_rebuild2.htm
Hope this helps,
Wayne