The earliest press cars were on a C plate, the majority of the road cars are on a D, and likewise the majority of the RS500's are on an E plate. The trim levels didn't vary (to the best of my knowledge), so all examples would have had electric windows from the factory.

As Jay said earlier, the only one to leave the factory in red was the one specially built for the Duke of Bedford, and that's currently up for auction (or has been auctioned recently), and was expected to fetch in excess of £70k, so unless this one is being sold for that kind of price, then I have more doubts on the authenticity of the seller.

If the date of manufacture is 1984, then it's likely to be a 1.6L 3 door shell (which would account for the manual windows), or possibly an XR4i with the rear quarter lights changed to look like the Cosworth.

The VIN plate should give you more clues about the engine, colour, transmission and trim. I've attached a photo of my VIN plate and the other plate on the slam panel (not sure what that's referred to as), so the one you are looking at (if it is a Cosworth) should look very similar.

Mine is a Diamond White car, so that's what the colour codes identify. The other colours are Moonstone Blue and Black. Not sure what their colour codes are but I'm sure someone on here will.

The two letters towards the end of the VIN number (in my case GA) denote the engine month/year of manufacture. GA equates to November 1986. This won't necessarily tie in with the date of first registration obviously, mine was in fact not registered until May 1987, but it should give you a good idea of when the car was built originally.
The 5 numbers after these letters are the engine number

Here's a list denoting all the month/year codes - https://www.burtonpower.com/tuning-g...ure-dates.html