Re-creating a Zinger Cake

I'd do just about anything for my sister...until now. My sister finds this recipe that is a re-creation of the chocolate Zinger from the 70's. Even though she has great baking skills, she realizes the time this is going to take, sooooo, a little begging later and no deadline; I decide (of course) to take on this challenge. I spent 4 1/2 hours today making what is basically a cake with filling. Granted, the cake is absolutely one of the best I've ever tasted. But the filling and frosting are crazy time-consuming. The end product is very yummy- filled with calories and not something you want to eat every day (it has shortening in the filling). But...I think I like having my sister indebted to me for at least a month!!! As for a new catering product- not so much. I'll keep this as a special family/friend recipe.