Everyone assumes you will be running 3 huge Rochesters or Carters, there is nothing in the rule book to say you can't use 3 smaller carbs like the performance versions of many European 6 cylinder cars did, if you size and jet the carbs right it will give you a nice even mixture distribution and a smooth running motor.
Possibles are VW Beetle Solex carbs, these have adjustable main jets available and a good choice of rebuilt examples, Weber 34ICH, SU's on a right angle adapter. Jeep 4 cylinder carter carbs which is a smaller version of the Chevy 6.
Dare to be different!
