‘66 Barracuda

318 all the way. 5.2 even better (heads). Loads more torque and HP than a 2bbl 273 and cheap as dirt. Cheaper to build too (almost no 273 pistons available cept stock replacements and the 1-2 4bbl options that are >$400 a set.) . Small bore V8 offers nothing a 318 can do better, cept maybe mileage at the cost of HP and torque. Keep the forged crank and put it in your 318 so it fits your convertor. 273 fast revving? 318 has the same stroke.....rev away. 360 will be more to buy initially but the same to build and will wallop a 318 in every aspect. 340s cost too much to buy nowadays for what they offer 'cept bragging rights. If you keep the 273, spend money on 3.55 or higher gears. And you can keep all the 273 stuff for all the blocks, no one will know the difference unless its got Magnum valve covers and even LA covers fit Magnum heads using 5 of the 10 bolts.