Are the frames the same? 05 crf 250r and a 07 crf

Would plastics on a crf 450x be different than on a crf450r 05

No. Honda has a very crafty way of making two different models look like they have parts that will interchange, when - in reality - they are totally different. That goes for not only the major components like frames, but for nearly every part, on nearly every model. Very little in the way of parts interchangeability.