Binggy, thats quite a broad set of questions there, my friend. We won't get directly into the big block vs. small block issue (hot topic - do a search
) but you are correct in your basic assessment that it does not take a monster motor with a ton of horsepower to have fun in a small, light car like the Cobra. A stock 302 or 351 Ford V8 with a few basic add-ons like a good manifold, cam, carb and ignition system will give you an easy 300+ HP and bolted into a 2300 to 2600 pound car will run plenty fast for most people without undue stress or longevity issues. Here's the problem, though. With a Cobra, everyone expects it to be ready to defend its badass rep, including the owner. Being quicker than most of the ordinary cars out there is sedom enough after the initial novelty of ownership; everyone with a hopped up Honda or a Mitsubishi Evo will want to challenge you. I don't recommend racing on public roads, but human nature will have you wanting to know that your Cobra can back up that rumbling exhaust note and threatening appearance. You're gonna want respect! Build it with enough power from the start especially as you live in a place that does not give you easy access to powertrain upgrades.
For a starting point in your search for info, visit the engine manufacturers listed here on the home page under "CC Advertisers". Look at the various engine combinations that they sell and note the performance parts listed and the resulting power that the engine puts out. Note which pieces you are interested in and go to a vendor's site like Summit Racing
http://www.summitracing.com/
and browse around for prices, specifications and alternatives. Good luck. What decisions have you made regarding the body and chassis?