OK so here is what I have done so far... I had also seen that recipe for fruit on top as well as others. I also found a few that used coconut milk or coco lopez. The party has an "island" theme so I liked the idea of using coconut. Didn't find coco lopez but another brand at the store. Also found this recipe which I thought was the most authentic for the "leche" sauce.
http://www.elmejornido.com/en/kitchen/recipe/116509/three-milk-cake-pastel-tres-leches
I just made a boxed yellow cake and covered the bottom of the 9x13 pan with chopped peaches. I went to the store for the coco while it was baking and when I got home it was "beeping". It looked very brown on top so I took it out and started poking holes with a fork... but when I got to the center it was still raw! Oops.. Should have checked it better. Put it back in and it finished cooking, just concave in the middle.
One recipe that I read had you replace all the sweetened condensed milk with the coco lopez. I used the above recipe and started to do that but only 7 oz of coco at first. I tasted it and it was plenty sweet and the flavor of coconut was strong enough for me. Then I added 1/4 cup of spiced rum instead of the brandy.

Next time I will add it only a tbs at a time. The flavor is very RUMMY! LOL Hopefully it will evaporate off some and the cake will mellow it out. (my 5 yr old is one of the guests of honor

)
I am just going to thaw out some cool whip for the frosting.