Combine first 7 ingredients in a large mixing bowl; mix well, and set aside.
Melt butter in a heavy saucepan over low heat; add flour and salt, stirring until smooth. Cook 1 minute, stirring constantly. Gradually add 1 cup milk; cook over medium heat, stirring constantly, until mixture is thickened and bubbly. Remove sauce from heat.
Spoon sauce into crab meat mixture, mixing well. Add toast crumbs, reserving 1/4 cup; mix well. Stir in mayonnaise.
Fill 12 crab shells or 6-ounce custard cups with crab meat mixture; sprinkle reserved toast crumbs on top. Bake at 400° for 20 minutes. Serve immediately.