As mentioned above, you don't have a ton of options as far as swapping engines goes. You could rebuild your current engine, or get the FSZE from
www.corksport.com or another site that sells it. The FSZE has 175 horsepower and 135 ft/lbs of torque, and is as close to a direct drop-in as you'll get. In order to make it work, you would have to get ahold of the Japanese model ECU.
Me personally, I would rebuild the motor with the Mazdaspeed pistons from corksport, and the Japanese spec intake camshaft, and have the intake and cylinder head ported and gasket matched, and bolt in the basic intake/header/exhaust. And while you're at it, get a better clutch, a clutchmasters or ACT stage one will suffice just fine. All of the above mods will keep the car nice and streetable and reliable, while adding a healthy amount of power.