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I'm posting in an old thread because finding these parts recently became an issue for me. I am refurbishing the floor pan on a '73 F-100, and there are 6 rubber/plastic body plugs that are needed, some of which are impossible to find without a part number. Two are oval plugs in the toe board, two are circles under the seats, and two are large plastic caps that cover cab mount bolts. After a long time at the Ford dealer with the old parts manual and a junkyard trip, here are the part numbers I found:
oval plug:380680-S
cirlce plug:377977-S
large plastic cap (1.75 inches):377356-S