Doors and roof must remain factory. Also rear guards if a wagon remain standard. If a ute rear guards can be fiberglass. What kind of car are you building? Cheers.

make sure you fix the design flaws in it then:
"The Insurance Institute for Highway Safety (IIHS) issued a safety report in 2005, finding that Ford Explorer (the two-door, two-wheel drive models) made between 1999 - 2002 had the fourth highest rate of driver death of the 47 SUVs that were part of the study and in a study the year before, the Ford Explorer SportTrac received the worst rollover rating of any SUV tested.Ralph Nadar's organization Public Citizen along with many consumer action groups are pushing NHTSA and Congress to recall the Ford Explorer. The problems with the Ford Explorer are just going to continue to increase as the fleet of these SUVs get older. As the suspension, springs, shocks, tires, linkage gets worn out and looser, the handling and stability of the Explorer will be even harder to control in emergency evasive manuevers and other everyday situations in which a tight responsive vehicle is required and expected. Further, Explorer lawsuits have been file in court alleging that the Ford Explorer roof is defective as the design creates a weak roof subject to severe roof crush or roof deformation in a rollover resulting in severe spinal cord injuries,neck fractures, head injuries, resulting in paralysis, brain damage and death."

and some more:

"Ford Explorer Problems - Ford Scraps Twin I-Beam Suspension System

When Explorer production began in early 1990, Ford was already at work on a redesigned version for the '95 model year. Among the biggest changes: scrapping the twin I-beam in favor of a short-long-arm front suspension, or SLA. The switch was intended to accommodate two other key changes: use of rack-and-pinion steering and dual air bags, Ford officials say. But the new suspension also made it possible to lower the center of gravity by lowering the position of the engine, a memo said. But that memo, dated March 26, 1990, said Ford had decided not to exploit the opportunity. The decision "to retain the . . . engine position minimizes the effect on other vehicle systems . . . but does not take advantage of the fact that the engine could be lowered with a SLA-type suspension," the memo said. "This decision was driven by early implementation and program cost."

Ford Explorer's Suspension - Creates a High Center of Gravity

With the new suspension system Ford installed in 1995 and later model Explorers, the auto maker could have lowered the center of gravity of the top-heavy vehicles by lowering the engine height, according to memos by Ford engineers. But the company decided to retain the original engine position, at least partly to hold down redesign costs and preserve profit margins of nearly 40% on the popular Explorer, the documents show. A Ford spokesman acknowledged a small rise in the Explorer's center of gravity with the '95 redesign, but said the difference is inconsequential."

You have a bit of work to do to make it a useful race car.
To be blunt you ARE starting off on the wrong foot, it's probably the worst rear wheel drive vehicle you could think of to put a big motor in and drive fast unless you cut everything off the chassis and start again.
On the other hand perhaps you might get some sponsorship out of firestone. :)