273 is it good engine?
In November of 1972, I blew up the original 273 in my 65 Barracuda at 150K trying to make it home from Charleston, South Carolina to Cochran, Georgia in second gear after I broke the 3-4 shift fork. My ship was leaving for Nam right away, so didn't have time to fix the trans before trying to get my car home for the duration. While I was gone, Dad replaced the 273 with a 340. The 273 with 4-speed would keep up with SS396 Chevelles through first gear (3.09 low gear helped here), but they would pull away in second and keep pulling away. Never got beat by a Chevelle or GTO after swapping in the 340.
A 273 has the same stroke as a 340, with relatively heavy pistons, plus even the hi-po 273's were given a pretty rinky-dink cam. So, at least stock to stock, a 340 is more of a revver. You want to keep your 273 for whatever reason, fine with me. I actually liked my little 273, and they can be built to make good power. But a 340 has 67 more cubes than a 273, and at the same level of tune will make 60-70 more horsepower than a 273, and will have a much stronger low and mid-range. That's just a fact. (These days, of course, with the easy availability of cheap Chinese stroker cranks, even 340's and 360's are little motors.)