Adjustable rockers necessary??

Hi, I am getting ready to build up my 340 with X heads. I will be using the XE268 from Comp. My machinist insists that I use adjustable rockers. After shopping around I don't really feel like dropping that kind of cash for them. Are they really necessary? Or will a new Mopar rocker set be sufficient? I imagine he is concerned with uniformity in lifter preload. Can that be obtained with non-adjustable rockers? Any advise would be appreciated.