Defiantly too much for what you have now... You can bore the stock carb you have now for a little bump in power!!! Boring it out to .650 is safe without worries of breaking through... Jetting would still be the same or very close to what you are running now.
The 390 carb. Needs at least 27/25 valves on the head with a good port and polish to get even close to running decent... The 390 carb is a bit of a pain to even get running somewhat right on gas...
If running Alky it is easier to tune the 390 carb.