True, but if that were the case, wouldnt you think they would offer the upgraded valve springs needed to run the 422 cam too?
I havent seen where it says to use stock pushrods anywhere, but what I can say is this.
Whats the 4.0 known for, push rod and rocker arm wear. What takes up the slack,the lifter. What happens when the lifter has no more room for adjustment, it cant compensate for the reduced base circles, let alone the factory cam. Now if you upgraded to Deltas hardened pushrods and rocker arms, the lifter might have enough travel to compensate. I cant offer any personal experience to that. Im not saying it can, nor am I saying it cant. But to someone, that might be a beginning to a recipe for success.
Bird beat me to it....If anyone knows, its him.