It will be like a governor on it. Also when you are just riding around remember you will be driving that 500 CI on those TWO tiny throttle bores in that center carb--not good imo
I did a back to back on a 600 HP unit like you mention--with a single four it was like a different animal--I am no six pack fan when it comes to the big cube units
Not to mention the long period of time and $$$ it will take to get it running suitable--there will be folks that stand up and say that they can/have made six packs run perfect but......most folks wind up pulling their hair out on those deals.