YOu really can only check them carefully. Are you running a roller cam? Flat tappet, Hydraulic? You MUST check the pre-load and geometry EVERYTIME to get it right. Small window of adjustment.
We have an actual checker that is labeled so you can see how long it is, An adjustable push rod alone will not do it unless you have a special fixture to measure them. Pushrods are not measured end to end because of the oil holes but on the 120* down radius. Our tool starts at 7.800 and goes up .050 for ever full turn. I can then get you pushrods in one day 98% of the time. If a customer buys a roller cam kit from us he can opt to buy the tool and tell us what size pushrods he wants which we will ship later at the kit price
Mike