(I corrected my first post typo on flow numbers).The heads on the 422 are econo W2's ported by Moparts member OU812, they flowed in the 285-290 range. I can't elaborate on the 426 heads but they flowed in the 275 range. Both have 1.5 rockers (although 1.6's might offer up a bit more power). The 426's exhaust manifolds have been extrude honed but on the dyno we tested them vs unmodified examples and there was only a couple HP difference. The intake is bone stock as is the Thermo-quad (4972) didn't even change the jets so nothing magical there. I'm sure some jet changing and intake porting would find more power.