A different tank for the commode
The tank to stool interface for most units is pretty much the same. So if it looks like the two holes used to secure the tank to the stool match up and the center water passage hole under the flapper valve is in the same location you should be good to go (at least in the USA). 

Re-using old seals can be a problem and lead to leaks. When you mount up the salvaged tank you should replace the bolt seals and the seal that sits between the tank and the stool. 

The reason the seals need replacing is that they harden with age, lose compliance and can even sometimes crack. Part of this relates to the chlorine in the water. The tank to tub seal also can take on a compressed shape and if the salvage tank is not exactly the same form and fit in the seal area you can have a leak problem. 

I would recommend getting a tank mounting kit that includes the seals and new tank attach bolts and throw the old parts away. Probably also a good idea to replace the flapper valve at the same time.