It depends on many variables,eg,different cylinder heads,number of valve jobs,production tolerences,etc.
As a personal example I needed longer pushrods when I installed Crane 1.7 pedestal mount roller rockers on my 89,with stock E7 heads.The heads had the valves ground once in the past.
You may or may not have to get longer pushrods.You won`t know for sure until you go to install them.
I suppose you could check how much preload you`re getting on the stock rockers now as an indication.
It depends especially on your cam and heads. You dont know until you do the install and check lash, preload, and make adjustments. Proper length can be found by the use of an adjustable pushrod tool, works wonders and cuts out the guessing.
It depends on the rocker manufacturer also. The only way to tell is to get an adjustable pushord ($12-16) and check for proper length - the right way/only way to do it anyway.