Do you have a pic of the type of lug nut your going to mimic? I have done a search and all types come up.
But, with all the pics that i have seen, if I had to make this I would probably start out with a hexagon pan to create the layers of cake and then go from there. you could cut a regular hole in the middle of all the cakes. Then i would put the dowels in around the cakes the same way you would do any other doweling, there just wouldnt be any dowels in the center bc of the holes
Stacked ontop of each other like you would normally and doweled and cakeboards inserted thruout depending on how high yr going to make it.
I would insert long dowels that have been sharpened at the end straight down the sides of the tiers. that will support them.
Im not sure how to direct you about the FACE coming out of the cake bc I have never carbved one. BUT, if you opt not to carve, mb you could make a face using a mold and create yr face from there.