WR-250F parts fitting a WR-250R?
Well, there's the...
*Oil filter element, although it is installed facing different directions due to a different engine with a different oil filter cover and a different oiling system.
*The WR-250F stock front sprocket will fit the WR-250R, but not vice-versa.
This is due to the WR-250F sprocket having a relief groove cut into the side facing the engine in order to clear the oil seal retainer not used on the WR-250R.
*The rear sprockets will fit either bike as long as the mounting bolts and nuts for the sprocket went with it.
*The tires would fit either bike.
Same for the tire tubes and rim bands.
*The oil inside the engine would work in either bike.
*Depending on the model year of the WR-250F, the headlight bulb (not the glass lens, just the bulb) could be the same.
My 2002 WR-250F headlight bulb is the same one, but the one that was in my (now gone to a new home) 2009 WR-250F was different.
Beside some misc. nuts, bolts, washers, etc., I can't think of anything else.
The two models are different - different chassis, engine, suspension, seat, fuel tank, plastics, the whole nine yards.
Personally, I think it's confusing and more than a bit rediculous somebody made the decision to call the dual-purpose bike a WR-250R.
Probably a marketing team of psychos.
XT-250R sounds more like it to me.