DJM, There are small differences in challenge car chassis, because its a challenge car with extra rollbars etc they are much stiffer then the street version to start with. I had a MK2 and added a couple of extra bars to update it to mk4 'spec'. There are also footboxe differences to accommodate newer wider engines in MK4.

As for Coyote it fits in the challenge car it fits but you will need updated the drivers and passengers footboxes to fit the super wide Coyote engine depending on the age of the chassis. These parts you can get from Factory Five if you ask for them.