Most of the fp and rb are about the same from what I found, there are a couple that are bigger on one end or the other but not both. Most are about .030" +/- .003". The biggest that I have found is actually a ballpoint, the Aero. There are some things you can do to keep things thinner but take some work.
An easy thing is when you put the hands on put the hour on first then cut the "hub" off the minute hand and just glue it beside the hour "hub". The "bridges" are harder but worth it, they add a lot of interest as they have all the jewel bearings. I file them down to about .025", thinner if you are using carbon fiber. Carbon fiber itself will take up half of the .030" that you have to work with. And last bend the parts as close as you can to the tube diameter. Being over bent or under bent will cause the parts to stick up higher.
Mike