Naked AV

It's been recommended to me to get longer than stock pushrods - 7.45" to be exact - because the cam I am looking at has a smaller base circle diameter than the stock cam. According to my source, this is to get the correct preload on the lifter (or something like that - sorry, I am pretty ignorant in this area). If not, I could have valvetrain noise, something like the 'sewing machine' threads I have read around here I guess. Does this sound correct? If so, why is it that no one seems to carry this length of pushrod (Summit, Jegs, Thunder, etc)? It would seem like this would be a popular pushrod if my case was common....