You could almost build two 318’s for the cost of a 273 and have nothing to show for it other than less power. The motor’s exterior dimensions are the same.Good luck with a 273 V8. It would probably be the best fit in the Valiant’s engine bay. With a little work can out so nice power BUT as rare as they are parts are twice or more times than the price of say a 318 and high performance items like a cam, pistons, etc are almost custom orders … you can find a nice selection of 273 parts at egge.com but a good block might be the pricy piece.