Pushrod for hydraulic cam and 273 rocker arms

50 year old iron
heads or block milled
lifter vendor have consolidated
just start over with an adjustable pushrod as Rat Rod has stated
do the mid lift method with the adjuster up as far as possible - you may have changed the lift, different base circle, milled this or that
mechanically you measure from the center of the balls but who does that?
sending the adjusted pushrod to the mfg gets you the correct ones
or it's on you to figure out how the vendors spec their pushrods - over all length, bottom of the cup etc
btw use AMC/Magnum lifters and oil the rocker adjuster balls or cups in the stock rockers through the pushrods
and if you have roller tip rockers move the shafts up and over
Crane used to sell offset shafts- must be a reason