Once you have verified everything is the right size (length and correct cup size) then you may want to look and see that enough oil is getting to the pushrod cup. If the pushrod is too long the cup can shield the flow of oil depending on the location of the oil hole.
Typically a lack of oil will turn the ball & cup black. If the pushrod cups are not hardened properly they could fail in the manner yours did before they turn black.
Did you restrict the oil passages to the heads? If so you probably should open up the oil passage some.
When you put it back together get a garbage valve cover and cut the top off of it so you can look and see if oil is flowing. Or just run it without the valve cover. Making a mess is better than not knowing if it's right.
Good luck
Bill