Four different pieces total: Doc & wheelbarrow, Grumpy & Happy, Sleepy & Sneezy, Bashful & Dopey. They stand about 1.75" to 2" high and came with hoops on the front and back so they could be connected together like a train.
Dopey and Bashful are pictured below.
Image via timepassagesnostalgia.com.
The Nabisco ad campaign was highlighted on page 3 of the 1967 US Merchandising Supplement (which accompanied the Snow White pressbook). The Walking Dwarfs would be placed in four million cereal packages. Plus there was a special deal where kids could mail in 50¢ and a proof-of-purchase to receive the complete set.
The original Rice Honeys and Wheat Honeys cereal boxes with the Walking Dwarfs promotion.
Cereal box images via theimaginaryworld.com.