The engine and in fact the complete powertrain choice you make for your Cobra is elemental for your enjoyment. All Cobra owners have pondered this. The advice given earlier in this thread about driving a small block and a big block is sound advice. Try both to get educated. Living and driving in a Metro area like LA will factor into how you set up either drivetrain. Im in DC burbs. I decided early on to Go Big-Block (460) or go home for my build. Its a personal decision. Im only building 1 Cobra. My Cobra. Your plan may differ.
When you start a big block, rev a big block and idle a big block it has its unique characteristics. My house shakes when I start it in the attached garage. Some owners may not like that. On Sunday morning my family “dont need no stinking alarm clocks”.
From my experience, my neighbors ( love them!) feel the big block Cobra approach along with hearing it. Its just different than a small block. High revving small blocks are loads of fun too but your choice of big or small should take into account what your goals are. Weekend cruiser? Short trips , long trips? Cam, intake, and carb (or efi) and exhaust choices will impact the drivability and fun factor. I set up mine with a 5 speed TKO600 that cruises on the highway at 70 mph about 2200 rpm with good fuel economy.
I typically travel 2-3 hours on a Sunday cruise. The motor is set up to really pull from 3,000-5500 and is deafening above 4500 rpm but Loads of torque and fun.
Dont take our word for it. Go drive some to form your own opinions and good luck.