the ex-500 frame is not interchangeable but, like mercenary said just ride it as is. just because it has a salvage title doesn't mean it has or had frame damage.just the cost to fix it was higher than a given percentage of the value by the PO insurance company.which with these and the 500 ninja's is usually attained by just a slow lowside or even a abrupt tip over, busting the upper cowling,blinker,scuffedmirror,scappes on the muffler, you get the idea.
As long as the 04' 250 you bought has a offical title that says salvaged by your states DMV no worries.Now if the salvage title you have is from the salvage pool the guy you bought it from, your kinda screwed you would have to find a clean title bare frame and swap everything over to be legal.Don't know if where you live is the same as where
i live but you also need the original engine number also so if you don't have that it's a paper work and fee induced nightmare that sometimes makes it not worth it.
All that being said it is the same scenario as how I bought my 2000 250 Ninja,just with out the girl friend quotient (my wife wouldn't like that part of it,lol)