Prepare a greased 9x13 glass baking dish, set aside. In a large mixing bowl, put in the milk chocolate bar pieces, semi-sweet chocolate chips, 4 tablespoons butter, and half of the marshmallow fluff. No need to mix. Set aside.
In a separate large mixing bowl, put in the peanut butter chips, 4 tablespoons butter and remaining marshmallow fluff. No need to mix, set aside.
In a large saucepan, combine sugar and evaporated milk. Bring to a rolling boil over medium heat. Stir CONSTANTLY for 4 MINUTES.
Quickly pour about a cup of cooked mixture into each bowl of chocolate at a time, stirring as constantly as you can for each bowl (you might want a helper for this part). Try to divide the cooked mixture between the two bowls as evenly as you can.
The boiling mixture will melt the butter and chocolate. Stir each bowl until all chocolate and butter is melted and the texture is smooth.
Scoop spoon fulls of each fudge (alternating about 1/4 of each type) into the prepared baking dish.
Using a knife, swirl the two types of fudge together to make a pretty, swirled design. Cover tightly and refrigerate until hardened (several hours or overnight).
Keep refrigerated until ready to serve. Store cut up pieces of fudge in an airtight container in the refrigerator.