Geiserbros racing is the ones who built everything except the body. They stated in a comment (which I believe was removed later) that it was built on an f150 frame with a 2.7 EcoBoost. Another one posted a picture of frame and stated it was a raptor front end. I don't understand where Ford is trying to lead us with this but these are what I am basing my assumptions on.I'm still not convinced the R was on an F150 chassis. Ford directly said:
"The race prototype is built on a modified Ford T6 architecture that will provide the base for the production model"
I am very skeptical that they would straight up lie like that (if they had said 'a body on frame architecture' or something more vague that would be different), and the only evidence we have to the contrary is some guy on a forum who says he saw it in a shop.