I spoke with Terry Manton at length back before he passed when I was putting together my 416 I was running a .690 lift solid roller with springs that had 742lbs over the nose.
My head and rocker combo would not allow a 3/8 push rod on the intake he assured me that his series 3 pushrod 5/16x.118 wall would do just fine and it did.
I shifted at 7800 every shift never a pushrod issue.
Now I did have a short deck height of 9.350 so that kept the pushrod on the short side but that motor is still together running great 5 years later and hundreds of passes.