ECJ's don't have an engine code. 8305 tells us it is a CJ5, the last 6 numbers are the serial number.
As far as the carb, the stock Rochester 2G series is one of the best out there. I would check to insure the idle mixture and curb idle are adjusted before you chuck it. If you're looking to go bigger, you will need a manifold to do it properly. Summit still sells them new, and used ones pop up from time to time. A small 4BBl will really wake the engine up. Stay with a dual plane for the best offroad results.