Do the 460, a good strong bottom end and some nice free breathing aluminum heads and intake will have all the snort the Ranchero will need..... Friend of mine is running a stock bore 460, Victor Jr. Heads, Holley Dominator, MSD "plug and play" distributor with a Comp Cams solid lifter cam.... Does 500 horse AT THE REAR WHEELS.... He's running it on E-85...... Detuned, smaller carb, and made streetable would be an easy 450 horse at the flywheel.