In a large mixing bowl, combine 3-1/2 cups of the flour and the yeast.
In a saucepan, heat and stir milk, granulated sugar, butter and salt till just warm (120 degrees to 130 degrees F) and butter almost melts. Add to flour mixture.
Add 6 eggs and vanilla. Beat with an electric mixer 30 seconds, scraping bowl. Beat on high speed 3 minutes.
Using a wooden spoon, stir in the raisins, orange peel, 1 cup almonds and as much remaining flour as you can.
Turn out onto lightly floured surface. Knead in enough remaining flour to make a moderately soft dough that's smooth and elastic (3 to 5 minutes).
Shape dough into a ball. Place in a very large greased bowl, turning once to grease surface of the dough. Cover and let rise in a warm place till doubled in size (1-1/2 to 2 hours).
Punch the dough down. Divide dough in half; divide each half into 4 equal pieces. For each braided loaf, roll 3 portions into 18-inch ropes. Line up the 3 ropes 1 inch apart on a greased insulated or regular baking sheet. Starting in the middle, loosely braid by bringing left rope underneath the center rope. Bring right rope under the new center rope. Repeat to the end. On other end, braid to center by bringing outside ropes alternately over the center rope. Press ends together to seal.
Cut the fourth piece of dough in half and roll each half into a 16-inch rope. Loosely twist the ropes together; press ends to seal. Place on top of the braid, lengthwise. Tuck all ends under, forming a braid that's about 12 inches long. Repeat shaping and decorating directions with other half of the dough.
Cover loosely and let rise till nearly doubled (1 to 1-1/2 hours). If you like, brush with beaten egg and sprinkle with coarse sugar and slivered almonds.
Bake braids in a 350 degree F oven about 30 minutes or till loaves are golden and sound hollow when lightly tapped. Cover loosely with foil the last 10 minutes of baking to prevent overbrowning. Cool on a wire rack. Serve warm or cool.