Rocker arm endplay

I don`t seem to have any end-play after I tighten rocker shaft nuts on heads.
I did a mock up with the shafts tight in box ,and spacers and washers tight against shoulder on other end. Seems to be enough end play. When I install on heads and tighten up ,end play is gone. I even tried without rubber seal ,zero end play and binding.
Could this be because the tins are slightly distorted and rubbing on thrust washers?
Has anyone else ran into this ? I was going to grind about .010'' off end of rocker arm ,but first I`ll wait for some replys.
Thanks in advance guys.

The stepped thrust washer goes into the rocker box casting before the rocker arm and with the shoulder abutting the rocker shaft. This is what creates the end play. The shaft and rocker arm should be the same length, the shoulder is the spacer! There is nothing except the tin on the other end held in place by the shaft as it is tightened. the tins should be perfectly flat in that area.
Robbie

Maybe that`s my problem ? There is no stepped thrust washer in the aluminum housing ,just a hardened flat washer.
The dimensions from shoulder to shoulder of rocker shaft(s) is about .010'' -.015" longer than rocker arm.
Does anyone happen to have the dimensions of those stepped thrust washers?
I could machine up a set of them ,to get me thru the season.
Thanks in advance.

Thanks Robbie,
I made a couple of stepped thrust washers ,now I got perfect endplay on the rockers . Now I`ll take the rear head off and see what that one looks like.