The 800 is a bit large for the engine. 750 would be my max size for it.
You did get the tuning kit for the carb right?
You also did not give a wholeot of info on the engine. What exact cam?
Headers?
Etc...

Depending on what your trying to do& have in the engine and the cars set up, converter, rear gear, tire size, etc.... You may even be able to use a smaller 650!