From the top surface where the bolt carrier stops (on the right side because the trunnion is reversed) at the trunnion to the top of the receiver on the right side would be approx. 7/8". If you have your rails installed a better way is to attach the gas tube, put the bolt in the BC and slide it in on the rails until the bolt head enters the trunnion and locks around a fired case then fit the trunnion to the rails and not the receiver top. If the rails are not installed, use the 7/8" dimension to mount the trunnion and fit the rails to the locked bolt head and BC.
Hope that helps. Getting the trunnion and rails at the right height to each other is probably the most critical and difficult part of the build.