The general rule of thumb says multiply the cubic inches by two .. then round up to the next available cfm carb size.
SO, no - you're not oversized, (yet).. LOL..

She oughta run good on a 780 or and 850 equally. As RSpears says, get the book for short money and you'll know how to tune the carb and get the best out of it. You'll also need a vacuum gauge and a timing light if you don't have'em already.

Enjoy the ride after, knowing you did it too.