To maintain the proper pre-load on the lifter given the following changes from stock you will have to change the pushrod length:
(a) Thinner head gasket (copper) will require shorter pushrod.
(b) Valve job which seats valve deeper into head will require shorter pushrod.
(c) Milled head to eliminate warpage will require shorter pushrod.
(d) Higher lift cam with smaller cam base circle will require longer pushrod.
No clean answer to your question. It all depends on your setup, headwork, cam, etc. It would be best to use pushrod length checker or use adjustable pushrod and measure length after installing at proper preload.
With bent pushrods, I would check your valve springs for coil bind given your valve lift.
Just some ideas.
Deep Enough
Donald McMullin
