Interesting indeed. Back to the question of the original topic - 390 for correctness, 460 for everything else you want
My F5R is correct in every way except for the color, body type, engine, gauges, transmission, wheels, tires, suspension, carpet, and oh yeah, the radiator. But you know what, I bet I have as much fun driving mine (13,000 miles in 3 years of ownership) as you do in your correct replica
Plus, 460's are easy to find parts for.