Slight differences in pushrod length can be adjusted out with the rocker arm adjusting screws. If it's too far off for that approach, most of the hot rod camshaft grinders have semi-finished pushrod sets that can be cut to length. I just built a set for a Plymouth 383 engine because I installed a set of roller rockers and the pushrods had to be custom-made.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!