If your rebuilding your 273, you might need an overbore and that means new pistons. I thought of this about 6 years ago, but didn't want to spend 600 dollars for custom pistons. 273's can run well, but 360's run better for less money.
As others have said - if you have to rebuild and are OK with things being non-stock, really think about all your options long and hard before choosing an option. There is a lot to consider and the more HP you have, the more other things need to be considered (transmission/rear-end)
Also, one thing to think about is the resale after all is said and done. Even if it's overpowered and you can't get traction, a 340/360 is always going to help things sell compared to a 2brrl 273.
