Originally Posted By 6T4 Polara
I believe somewhere mid 63 they went from 4 to 6 bolt.
You did not state what year you need info for.
Not so, they went to the six bolt valve covers on all the heads in 1964, Max wedge or 361 two barrel motors shruggy
Mopar did make a limited amount of 425 HP Stage Two 426 in 1963 for drag racing only, bigger carbs, bigger cam, hand modified combustion chambers on the 286 heads for better flow and hand modifeid intake manifolds for the the bigger carbs. scope

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)