To distinguish original SB oil pans GM #3820000 ("5 quart") and 3820001 ("6 quart") from their circe 1976 SERVICE replacements, GM #360866 ("5 quart") and GM #359942 ("6 quart"), do the following:
Lay a straight edge across the front oil pan rails above the front seal radius. Then, measure from the BOTTOM surface of the straight edge straight down to the APEX of the seal radius (i.e. from the bottom of the straight edge to the CENTER of the front seal radius). If the measurement is 2-1/4", the the pain is of the original variety and requires the 63-74 style gasket or gasket set. If the measurement is 2-3/8", then the pan is the circe 1976 SERVICE replacement of the above-referenced part numbers and requires the 75+ style gasket or gasket set.
The same measurement can be used for C1 oil pans. If the measurement is 2-1/4", then the pan is an original and requires the pre-74 oil pan gasket or gasket set. If the measurement is 2-3/8" then the oil pan is the circe 1976 SERVICE replacement pan of GM #360867 (1956 only) or GM #359937 (57-62) and requires the 1975+ gasket or gasket set.
Lay a straight edge across the front oil pan rails above the front seal radius. Then, measure from the BOTTOM surface of the straight edge straight down to the APEX of the seal radius (i.e. from the bottom of the straight edge to the CENTER of the front seal radius). If the measurement is 2-1/4", the the pain is of the original variety and requires the 63-74 style gasket or gasket set. If the measurement is 2-3/8", then the pan is the circe 1976 SERVICE replacement of the above-referenced part numbers and requires the 75+ style gasket or gasket set.
The same measurement can be used for C1 oil pans. If the measurement is 2-1/4", then the pan is an original and requires the pre-74 oil pan gasket or gasket set. If the measurement is 2-3/8" then the oil pan is the circe 1976 SERVICE replacement pan of GM #360867 (1956 only) or GM #359937 (57-62) and requires the 1975+ gasket or gasket set.
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