318's thicker ?

Same sand cores as 340/360's, but smaller bores ? Building a Magnum 5.2 with mech. roller cam , "Eddy's"and steel crank. Sports car, 2,400 lbs, Dakota V6 bh. and Turbo Supra 5 spd., direct fit. Try not to chirp. Will need 7k + rpm. Ideas ? Thanks, Art.:snakeman: