71 Dart get 408/ Trick Flow Heads....

Don't know anything about the fast rate Howards/Hughes cam lobes, buuuuut if they max out the total available rate of lift of the 0.904" lifter diameter, then they would need lifters that are not chamfered to work with those lobes. Using chamfered lifters would allow the edge of the lifter to 'dig in' to the lobe.