Need Help building a 400 for my 68 plymouth valiant

They cut the 440 crank mains down to 400 size so you can keep your 400 caps and I think you keep your 400 rods. It may be cheaper to get lighter aftermarket rods than rebuilding your stock ones. Did he install hardened seats in the 906's? The 906 didn't come with them but the 452's did. The BB will require a different radiator,hoses,fan,pullies,driveshaft,better axle and disc brakes if you want it to stop. The 727 should be ok with a performance parts rebuild.