well ok, since you asked for opinions...
First- What is your current 302 engine's compression ratio? That number plays an important factor in deciding on whether it could manage the AFR 185 heads, or whether the 165's are a better choice. it is also a factor in determining if your 400 flywheel HP goal is reasonable.
Most stock, street 302's with 9.0-9.5 compression ratios are indeed best suited for the 165cc heads, but if your 302 has 10.5:1 compression ratio (or larger), then the 185 heads would probably work just fine on your engine (and would be one less thing you would need to upgrade when you step up to a stroker engine)
Regarding cams - There are many factors to consider, like: how choppy of an idle can you tolerate? is raw performance the primary consideration, or are you looking for more of a balance between performance and driveability?
for an engine that is primarily street driven, and needs to start easily when cold, you are probably going to be best off with a hydraulic cam, with duration in the high 220's to low 240's (at .050), and lift in the 555-570 range. If emissions and idle quality are not primary concerns, then a lobe separation angle of 112 (or even 110) will help generate a nice, flat torque curve... Something like the compCams XE274H, or the XE284H if you can handle a rougher idle.
A well-tuned 302, with 10.5:1 compression ratio, AFR 185 heads, and the XE284H cam would probably get pretty close to your 400HP goal at the flywheel, and would be a high-revving engine (7000+ rpm)
A similar 302, but with lower 9.5:1 compression, could use the AFR 165 heads, and the XE274H cam, and would probably dyno around around 360-370 HP at the flywheel, and would probably rev up into the 6000-6500 RPM range.
please reply back with your engine's compression ratio, (and the number of miles or km on the engine) so that a better estimation for your engine can be made.
also, a great place to do more research about small block Ford Windsor engines is on the many Mustang forums on the Internet. Any engine that works well in a Mustang, will work even better in a Cobra...