I'm leaning towards the Challenge car for my build. It will driven street mostly with about 5 track days a year to begin with. I may get competitive down the road but will stick to HPDE to start. My first question is can I use the mustang fuel tank. I will upgrade down the road to a cell but looking at them now they are retarded expensive and not in the budget. The second question is about the car not having the center spine like the MK4. How does that effect everything? It looks like it would make the trans tunnel flimsy without any structure under it. Curious why it doesn't have one. Have any of you welded one into the car?