Well stated and right on.
When Best Machine built my old 422w5 motor Chuck Millen gave me a great lecture about using as big a pushrod as will fit. With my X block we used 3/8 on intakes and 7/16 on the exhaust.
That motor was built circa 2004 and is still campaigned by the current owner. It has seen hundreds of 7500 rpm laps and never any pushrod issues, ever
Those same Manton's specced at the above diameters are still in the motor.
Regards the OP, we're it me, I wouldn't use a 5/16 pushrod in a roller with significant spring pressure. Probably would not have used that block that so limits your choices.
Might get away with it, but, IMO, that is tan extremely weak link. And weak links generally rear they're heads at some point.
I wouldnt recommend a 5/16 if a 3/8 cant be fitted
in the area but I HAD to go 5/16 due to the area..
I messed up by not getting offset intake lifters but
so far the 5/16 are working fine to 7400 rpm and that
might be going up
