The 500 2 bbl will need very little done to it. The power valve channel restrictions(PVCR) are very big and can flow alot of fuel as is. Make sure any carb you use has a black Nitrophil float, it will not crush under boost.
If using the 390 4 bbl double pumper the PVCR channels will need opened up to allow more fuel flow. They are small as the carb comes out of box. This would be a better streetable/ responding carb.
Either one of these carbs will limit your hp though. Probably to around 350 hp or 5200 RPM because of restricting air flow. If that is all the rpm you seek then they are good. If you want more than a 600-650 Holley double pumper is for you. Same basic mods need to be done to the 650 size carb, PVCR upsize as needed, block choke rod, nitrophil floats, jetting. Tom
