While it is not exactly rectangular,
The overall radiator shell dimensions are approximately 21.5 inches wide X 27.5 inches tall.
The dimensions of the radiator shell opening is approximately 18.5 inches wide by 19.25 inches tall.
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Matthew C. Hinson
1929 Ford Model A Phaeton, 1976 Ford Country Squire
AACA, MAFCA, MARC