You will almost certainly need the 2.6's
complete electronics package to make the motor happy in its new environment. It's very unlikely that you could just link up a 2.6 to all the computer engine and transmission management stuff that came with your car.
You probably need to keep the motor wed to its original transmission, too.
And then there are all those thousands of unexpected little details which make any hot rodding project so interesting, exciting, and expensive.