Better read this. You can use a 650 but this shows that you will be
45 hp down compared to the 850; almost as much as on a 750.
That's why I surmised that a 750 would be the conservative choice.
Keep in mind that the test engine didn't even have the Edelbrock heads.
Also, 1970 383 Roadrunners came stock with a 700 cfm Holley.
I stand by my initial recommendation, Just needs tuned to the engine.
I'm awaiting comments - 45 hp is a lot.
http://www.moparmusclemagazine.com/techarticles/engine/mopp_1207_carburetor_dyno_test/viewall.html