I'm not sure what casting numbers will tell you (unless is not a 350). It's kind of moot, it’s likely been rebuilt. You’d have to take it apart. Casting #s don’t tell you bore, stroke, cam, etc.
Start with basics. Check for & plug all the vacuum leaks, get timing set right (I’d probably do cap & rotor too), and get the carb adjusted. Too bad you didn’t do compression & leakdown before the headers went in.
http://www.edelbrock.com/automotive/....html#contents
Has it got an HEI or points?
Diva, ZZ4???