People almost give away 273's because they are hard to get rid of...
Most part them out and get money for the commando valve covers and adjustable rocker arms, and the forged cranks...
You can also use a 318 and it will look just like a 273, have a little more power than a 318, the 318 will bolt in exactly like a 273 with the same motor mounts, and they are cheap and available all over... :D