my 2.29 gears were common in the 78-79 cars. service manual lists a 2.19 or something like that. never seen one of those.
i once had a 400 sbc in a 79 cutlass, turbo 700 and 2.29 gears. drove to california and back. got 21mpg. but my girlfriend got better, 21.5-22mpg, and she drove faster too. god that pissed me off. lol.
if you want to stick with a v8, i would look at a 4.8l LS motor with an overdrive trans, (manual or auto) and some freeway gears. plenty of power and the latest in head technology.
but if you really want to turn heads, grab a late 80s, early 90s ford 5.0l with od trans, good for 27-29mpg. i worked for ford, heard many first hand testimonials from coworkers, customers and friends of their fuel economy. didn't matter if it was a mustang owner, crown vic, or lincoln town car.