I'm like Desert Dog and Kenc. You didn't even mention the 292. Why? Too heavy or some other reason? What about a high performance 327 from about 1965? I think a carburetored one was available in a Corvette with about 340 hp. I had a '65 Impala SS with a 327/300 hp that ran good and got 20 mpg but the handling was so unaceptable that I only put about 11,000 miles on it before trading it off. I never again took my brothers' advice about what car to buy. Does the 350 that came out about 1967 meet your qualifications and is a small block 400 too heavy?. I am not a mechanic and have not devoted any study to the subject; just mentioning what seems to me to be viable answers that would give good performance and good gas mileage.
