If you are putting it on a P250 Vintage style, it is not likely to work.
I it is for a P250S (sport), you have a better chance of it working.
The vintage style bike has a one piece exhaust header/muffler assembly that goes from the engine to the back end in one complete welded piece. The P250S and B&W and others have a header assembly IIRC.
EBAY sellers are not known for being to most honest.