Pushrod length with stamped rockers on Magnum

watch the utube vids on "rocker arm geometry". the one by straub industries is simple/good. with the cam at 1/2 lift you want the rocker at a 90 deg right angle to the valve stem THEN you get the right pushrod length to take up the space between lifter & rocker. EDIT its harder to scribe the horizontle line on the OE "sled" type rockers but you can do it