Can I install the logic board on my A1261 A1212

Simone - On the most part upgrading logic boards between different series of systems often doesn't work. You are better off locating a used system then taking the risk of buying a part which you may not be able to return if it doesn't fit or work. Even though you would think because the external look of the system is the same the layout internally can be quite different. The mounting posts , the fan & cooling system is different, the connection points for the keyboard & display may not be the same and in the case of the display the driver logic may not be compatible. And lastly think about costs and if you were to sell your system what you would get for it. Which is the major reason not to make a frankenstein box.