Per the title, Bundles for Britain was a World War II relief effort in the USA to assist war torn Britain.
Mr. Drysdale tells the Clampetts that their fortune now amounts to $80,000,000.
Starting with season seven, Raymond Bailey and Nancy Kulp are now included on the opening credits and were no longer listed as feature players on the end credits.
The 80 million dollars (in 1968) would be the equivalent of about $595,634,482.76 (nearly 600 million) in the year 2020.