Clarence - Yes, you have a fan governor back. I've been told some Cirkut shooters liked them better than the newer internal governor - they (maybe) run smoother, and you can make larger fans to give slower "shutter speed" effect.

Your lens is the double convertible, not the Turner-Reich triple. I don't know anything about the Centar, but suspect it will be just fine for contact prints. Did you get the ground glass back for the Century body? The Cirkut Attachment can be removed and replaced with a 5X7 sheet film back. so you can do both Cirkut and 5X7 with the same camera. It is also to view and focus when setting up a Cirkut shot. If you have the 5X7 back, you can do a couple of test shots with the Centar lens, if the shutter is somewhat functional.

As to making your own gears and tripod head, it should be an interesting project. Did you see the article a few years ago in "Home Shop Machinist" magazine about making a hobbing attachment for a milling machine? I don't recall if you only need one hob to make all different tooth gears of a given pitch. I know with involute gear cutters, you need several different ones for a range of gear teeth numbers. That would sure make it simple if you only had to buy or make one hob.
My notes show the ring gear for the #6 Outfit is 9 1/16" pitch diameter, with 290 (or maybe 296) teeth. That should give you an idea the approx. size you will be dealing with. I think the original was made of hard brass and nickel plated. You will also have to make a turntable of some sort.

Doug - I have a feeling the aerial film is the only real B&W option right now. You might contact B&H and/or Kodak about "real world" availability of these films. Just because they are listed doesn't mean they are still available, at least anything that is close to being discontinued. I've been curious about the demand for 9 1/2" film for aerial photography. Maybe there is still a market out there for aerial mapping. I've searched on APUG forum for aerial film information and there is some, but there is a lot of unrelated stuff to wade through.

Did you see the #8 Outfit on eBay that ends a week from today? It looks complete, except the lens is missing. The gear set is probably for a 10 1/2"-18"-24" Turner-Reich lens, which do show up on eBay now and then. There is no certainty a different T-R will work with this gear set, but chances are it will. Your original idea of getting a #10 is good, but #8s are easier to find, and usually cheaper by several hundred dollars. 9 1/2" film has to be cut down to fit an #8 Cirkut, which is a drawback. It may be a "#8 in the hand beats a #10 in the bush" choice. And if an #8 sells cheaply enough, that helps make a decision. But if you are willing to wait a few months, or a year or so, a #10 will likely show up. Of course, if you are fated to go down the Cirkut road, you will end up with more than one of them, so starting with an #8 isn't a bad way to go.