I think gains using just one cam would not be all that great. Also best to go with aftermarket head.
ECU should be on passenger side sorta behind the glove box with a bracket on it. Have to remove bracket to see the code.
The intake manifold should bolt up. If it has EGR port or some crap on it, I'm sure you could just block it. Too bad all cougars have VCT, EGR rocks!
If you're gonna do something, do it right the first time.
