blown bbc prop ?'s

Hey Jim...I have a 21' Cheyenne v drive daycruiser with as powerglide and 29% gears in a c500 casale...motor is a Greg suyenaga built 498ci 671 blower making around 800-850hp....I have an unmarked prop that I measured at 12" diameter 3 blade the pitch is somewhere around 17 or 18 if I had to guess...my question would be what prop should I run a 2 or 3 blade...and what size and pitch...it's mostly a river cruiser that I hot rod around...I want more of top speed rather than holeshoter....thanks...