Are you sure the block isn't 3830814? and not 3880814?
Block# 3830814 (Z-11)
Year used: 1963
Model: Passenger car
Engine: 427
Horsepower: 435
Bore: 4.313
Stroke: 3.65
Main Journal: 2.50
Rod Journal: 2.20
Notes: This block was used for all 409 applications in 1963. It is identical to #3798962 except that the cam valley area and area behind the timing gear has been redesigned. This block has the "X" on the front. This block was also used for the Z-11 427 engine.
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Block# 3830814
Year used: 1963
Model: Passenger car
Engine: 409
Horsepower: 340,400,425
Bore: 4.3125
Stroke: 3.50
Main Journal: 2.50
Rod Journal: 2.20
Notes: This block was used for all 409 applications in 1963. It is identical to #3798962 except that the cam valley area and area behind the timing gear has been redesigned. This block has the "X" on the front. This block was also used for the Z-11 427 engine.
Pics: