If you can, I'd recommend visiting Westwood Embryos in Waverly, IA. Doc West put together what I think is a really handy setup for cows. Its not fancy or complicated--it just works really, really well for working cows right in their pen. Each pen has a head catch and a gate to swing over to make a chute. In addition the walk gate into each pen opens into the back of this area. Jim told me that the cows never leave the pen for shots, etc. when they are synchronizing, etc. That really cuts down on the stress for the cows. I can't see any reason the pens wouldn't work just as well as a calving pen either. A visit is well worth your time to see how they set up their pens and pastures. Great folks, too!!
Another thought I'd recommend is to include a some self catch stanchions in the group pens. I give most of my shots to cows without ever going in the pen by just putting some feed in front of the four stanchions I have mounted in the group pen, letting the stanchion catch the cow as she comes in to eat, and then just flipping the release after I have given her the shot. I also use this to put in most of the CIDRs right in the pen. I saw these stanchions in the dairy equipment area at a MN farm show. They are used in dairies in front of the dry cow feed bunks, etc.. They are made in 8 foot sections of four and they could be cut down as singles or doubles if you choose. If you wanted to be able to catch more than four at a time you can buy multiple sections and they fit together on the ends. Absolutely the best investment I've ever made for working with cows or catching club calves that don't want you to halter them. Relieves a lot of stress on cattle and Iowegians!!