273 power? HOW?

It depends on what your goal is. If you want a motor that looks the same as the 273 - then a 318, 340, 360 can be made to look the same by using the external parts, like the chain cover, water pump, alt brackets, pulleys etc from the 273. What I did was drop a 318 in mine with all the 273 stuff hanging on it.

I have not looked into buying new pistons for one of these motors recently, but I bought two sets off of ebay a few years ago that were brandy new, a 060 and a .030 set for a 273. The .060 cost $20 for eight !! The .030 set cost 100$ with new rings. These werent anything special, just regular dumb old cast (new) 9:1 pistons. The deals are out there if you are willling to look.

What I'd suggest doing, if you want to keep the 273, is rebuild it using a 9:1 set of pistons, rebuild the heads with hard valve seats on the xhst, a mild bowl and runner port job, and a stock 340 cam with a dual plane intake, or the oe 273 4bbl intake, and no more than a 600 cfm carb with headers. Should be good for 275-300 hp.

Have fun deciding - remember it will cost about the same to do any of these motors -