How would YOU make a tire wedding cake?

Anyone have any ideas on how to do a cake like this?

My husband and a good friend of his want to make a tire wedding cake (a "man's" cake) for the friend's brother's wedding. They thought that it would be funny. I guess you could consider this a spin off of the diaper cakes, etc. We have a month to have it completed.

Here are the ideas so far:

1. Get 3 older small tires (they should be cheaper), 3 different sizes of course. Attach them together with nuts and bolts.

2. Ice it with drywall mud.

3. Topper: "Michelin Man" Bride and Groom.

Now from what I can figure out, we need ideas on how to make the Michelin couple for the top (I figured maybe mini marshmallows might work, or maybe clay?), and how to make flowers out of "man-type" stuff. Car related "ingredients" would be the best. He has loved his cars very much in the past, so it is fitting. Any ideas or revisions would be welcome!