That could actually work, depending on the wear on the cylinders. 2 barrel pistons are not a problem with a 273, they can easily run 9+ compression ratio with 64-67 heads. Rings are easy, just call Total Seal. They will make rings for any bore size you want. If the cylinders have very little wear, you could just hone with torque plates and be very good to go. Just don't order any parts till you know if the block will clean up with a minimum hone. As for vastly bigger engines, once you start down that road, you are talking about replacing the whole drive train. Starting with the bell housing and ending up at the 7 1/4 rear. The trans should be good and the headers may have to go if you run large exhaust ports on the early 340 or 360 heads. Barracudas only need Formula S badges.