I would not use a towel and a mallet alone.
We installed the ones on my Super Bee by wrapping a towel around a 18" section of 2x4.
Lay the 2x4 along the trim and hit it lightly with the rubber mallet to roll it over the lip.

*1969 383 4sp. Super Bee
*1966 Alfa Romeo Giulia Sprint GT
*1965 Porsche 356C
*2004 VW Passat Wagon
*2004 Mini Cooper S
*1967 Jaguar E-Type FHC



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