I'm glad you brought that up, because I asked Van's that question in my email too. Their response was if I was certain the elevator trailing edges were in trail with the stab, and if the trailing edges were even, then go ahead and drill. I've read several builder's logs about this issue. The consensus that I'm coming up with is that its better to have the elevators swing freely to verify that they are in trail. I've read that many people clamp down the counterweight arms to the HS and call it in trail (those tabs have mine effectively clamped down now). The problem, it seems, is that some amount of twist can be introduced during the construction of the counterweight arms, so they might look even with the HS, but the trailing edge not be in trail with the extended chord line of the HS. I'm not going to get in a hurry to trim the tabs just yet. I'm going to tweak the alignment of the rod end bearings, and do more research into how to check the alignment with the extended chord line. I've seen it suggested to wait until the tail is mounted on the fuselage before drilling the control horns for this reason.