I believe you probably have an A12a engine of 1237cc. Look at you serial number and it should start with the A series number. A12, a12a, a13, a14, or a15. Many modifications are possible, including going to 76mm pistons which I believe brings you to 1280cc. A popular upgrade is to get A14 (1400cc) pistons for this upgrade. The head can be ported & polished and you can change Carburetion. I am building a Locost 7 with a A12a engine and am using twin side draft Delorto 40s.
I believe many of the parts for A series engines are interchangeable.

Look on a dally basis on this forum for upgrade ideas. I assume N. Alabama is in the USA? Many of the people here are from Australia, NZ, SA as well as other parts of the world. Many options are regional. EBayMotors is a great way to look for parts. search for "Datsun (1200, a12, a12a, a13, a14, a15, 210, b210)" and then do it again with Nissan instead of Datsun.