What are the barrel lengths?
Trade for the 14-3 and forget about re-bluing the 28-2.
The reason for not re-bluing the 28-2 is because it will only go down in value once it's re-blued and you will never recover your money if you sell it.
I own many Sig's and S&W revolvers and in my mind the Sig you are talking abut is worth more then the 14-3 which can be bought in the USA for around $400 to $425 so it's doubtful I would trade him straight accross for the Sig.
Just my 2 cents worth
Your Sig P220 is not in production anymore. Depending on its condition it is probably worth much more than the 14-3. I sell P-226's for $825 in northwest NJ. The amount of accessories also plays a part in the price (mags, leather, ammo, etc). The 28 with a tiny rust spot that can be cleaned and cold-blued sounds like a better deal and you can keep the Sig (I like Sig's).