273's use all the same parts as any small block, except pistons. They have forged cranks and typically the crank does not need turning, just a polish. They run mechanical cams. The pistons are typically .020 in the hole. The heads are closed chambers and flow better than any 318 head as cast. With a good rebuild they make almost the same HP as a "back in the day" 340.
However, if you wanted to put a larger engine in place of a 273, Use the 340/360 heads, add the extra expense of headers. There are base plates that have the standard large opening to allow the use of the Commando air cleaner. Use an Offenhouser single plane intake and a 750 cfm AVS. Use the Commando valve covers. Now you will easily over power any tires you can fit on the back of a 66 Barracuda.
