Ray - the 420s is the factory suggested carb to replace the original on the 1937 216. Calibration should be about as good as it gets.
If you really want rods, they come up on ebay fairly regularly; and I am told the grumpy old hillbilly in Missouri can custom cut them to any specification.
A bit of trivia: we sold a set of 574s W-1's to a gentleman that was tired of the Johnsons on an early V-12 Cadillac. He stated the car had never run nearly so well on the originals
Jon
