My 273 Experiment
I'm in the middle of building a 273 for my Dart. I've learned that there are not a lot of options for pistons and they are expensive. You end up with a smaller motor that costs more, weighs more and makes less power. Since it's going into a Colt, originality is not a concern so you might as well build a 318. All the 273 dress up parts will bolt onto a 318 and nobody will be able to tell the difference unless they look at the numbers on the side of the block. Sorry to be a downer.