At least 25 more hp.Jim's 12 ports have been dynoing in at around 80 or so hp,All of wich is useable.
It is gonna depend alot on your commitment to tune the motor and buy the parts it will take to let the motor flow and rev.
Wesw has a good dyno chart from his 12 port.
Listen to these other guys,they have plenty of time with a 12 port.