Slice the bread, cutting through the bottom crust only every other cut, to form a "pocket" of two thin slices of bread connected at the base with the crust. With a mixer, blend the almond paste with 1/4 cup of the cheese until smooth. Add the remainder of the cheese and mix well. Stir in the grapes with a spoon so they are not bruised. Set aside.
Whisk together the eggs, milk, sugar and salt in a pie plate or shallow dish.
In a small saucepan, melt together the marmalade and the water. Simmer until just syrupy. Keep warm.
Spoon a good amount of the grape filling into the prepared bread pockets, smooth to the edges and press lightly to flatten. Continue with the remaining bread and filling.
Heat a griddle to medium heat and lightly grease with butter or oil. Dip bread in the egg mixture and turn to coat lightly. Fry the French toast slowly, about 4 minutes per side, until golden brown on the outside and just warmed through. Keep finished toast warm in a 200°F oven while cooking the remaining toast. Serve warm with syrup and a sprinkling of almonds, if desired.