If what you've got is a 273, then use it. The 273 in my '67 B'Cuda is a BEAST, but it was built up pretty good. Some of my specs are fuzzy becasue it's been a while, ironically not many miles, though. Here's what I did:
* .030 Bored out
* Machined a set of 1985 CopCar (actually 5th...