Mark, 1 3/4" tubes on the L78 cars with 4 speed....2" tubes on the 454 block in the 68. Factory reverse lockout worked ok with both the factory muncie shifter and a hurst. We welded a looped tab on the header tube for the clutch return spring
we used ceramic coated on the 68 car...Hooker Comps....ordered them plain, dry fit to chassis first, made our dimples for power steering, etc..then sent them out for coating....they work great. Definately worth the performance gain...smaller tubes on the 396 is the way to go...make for better low-end power...these engines like to breath...especially from 3,000 rpm's up
wilma