It would, of course, be a lot less work to simply replace the L6 with another L6 assuming that the trans is in good operating condition; but, how do you know what the trans is like if the engine is dead? Are you willing to make the engine swap with the possibility of needing to remove everything a second time to replace the trans?
Keep in mind that your car has the 250 ci engine, also called a 25", (or at least should have) so you will need to keep in mind what engines you consider.
Keep your tape measure handy as you poke around the bone yards if a newer engine is considered; most ohv I-6 will be much longer than the L6.