[bigblockv6]

The one barrel did not work out well with the 305 engine by 1961 the 305D 2bbl engine came in to replace the 305A even though it was still available. 125 net horsepower to carry around that much weight was really underpowered for the 305. The 2bbl brought it up to 142 net horsepower then with more improvements for 1966 to 157 horsepower. Possibly mileage may have been why a 1bbl was used. Originally the prototype trucks used were lighter 1958-59 trucks and the 1bbl version was more than adequate.