First, for your headspace; choose the brass you're going to use and measure the rim thickness in 4 or five different spots on several rounds.  You can then set your rim depth at the maximum measurement that you find.  There are also standards for rim depth with many cartridges. For example, the 45-70 is .070".  Then give your breechblock/barrel fit .002-.003" clearance.  Everybody though will have their own ideas about this but as Chuckster mentioned, you can have zero on the barrel/breechblock but if your rimcut is too deep, you're going to have a headspace problem.
As far as tightening up the barrel, Winchester used to set them up so that you had to use a wrench the last 3/8 of an inch.  Another good smith that I know has a different idea though and that is to have it snug just the last 1/8 of an inch and then uses blue locktite.  He feels that he does not want to put stress on the receiver and his rifles do shoot.  If you're doing this yourself, pay particular attention to your chamber.  Have the correct fitting floating pilot and dead nuts zero through the headstock.  If not, you could end up with an out of round chamber.
Now take this all for what it's worth, as I am not a gunsmith but I have listened to a couple of good ones discussing this while standing around at the shoots.  Hope this helps.  Bob

I like to set them up tight, maybe 1/16 of a turn. But I have noticed on bolt actions that when setting the barrel tight that the chamber will shrink a little under the threaded area. This comes up when setting the head space as I allow the last .005" to be cut after the barrel is screws into the action and notice the sides of the reamer will take a little out. When doing rifles without much shoulder on the barrel like a 94 Winchester with an octagon barrel it is a good idea to have very close fitting threads. If you try for 100 pounds of toque the shoulder will be gone.

Here are sme things to remember regarding threads (all threads):

1. If you use a interferance, thread fit, you take a chance on thread galling. No clearance = no lubrication. The only lube that will remain is that on the rougness of the machined surface and what ever mis-match there is in the thread angle. Niether are good options.

2. If your looking for surface area contact, you won't get it. The thread will always be loaded on one side once there is any torque applied. Even if you where to use a interference fit, both sides of the thread can't have even contact pressure.

3. If your trying to keep the barrel centered as well as possible, it won't matter, because the thread angle will cause the thread to center itself.

For myself, regarding torque, I use a 15" lever and tighten so that I know it won't hurt or distort the action frame. I also want it to come back off w/o hurting anything. My guess at the torque that I use is 40 - 50 ft lb.

Frank

Now Takedowns. The Winchester Takedown system is well done. I suspect that many if not all Takedowns were finished in the Custom shop. I have mixed Takedown Barrels as they came into as many as three different actions and with the exception of having the correct Extractor they all went together by Hand as they were supposed to. There is however a Takeup system for adjusting the tightness of the fit. It is sensitive, if you get crazy the fit will show it. Now I make no claim that a Takedown Hiwall will be competitive in serious bench rest shooting. But in Offhand completion with the rifle in good order and a good load they will shoot better than most if not all Offhand shooters. Their is no need for action wrenches
or vices to take them down and or assemble them. I own two schuetzen and three sporting Takedown rifles and they work fine. This is my view and observation in over 50 years of actively chasing and following M1885s. Some with experience.
I have one Hiwall in which nothing fits right. It was rebarreled by CC Johnson around 1953 to .222 Remington and I believe he re threaded the receiver as no other Hiwall barrel I have will
screw into it anywhere near correct. HTH. Regards, FITZ

Oldtimer- You are correct in that one of the thread-fits that I mentioned, that I had heard was good to use, was one where the thread-fit was so tight that, to initially screw the action on by hand, required a fair bit of effort by hand. This is as opposed to a thread-fit where the action screws on easily and you can lift the back of the action up and down slightly before the action's face meets up with the barrel shoulder. My next question was about how much final torque/degrees of rotation was best for the final clocking-alignment of the action to the barrel. Other's comments so far have been that this can vary from 1/8" to 3/8". I think this may translate to 5 degrees to about 23 degrees of final rotation.

The least area of metal is usually the shoulder of the barrel shank and the corresponding spot on the receiver. Would expect it to compress somewhat when the barrel is torqued in place and reduce the barrel to block clearance. Have read to allow .002" compression, but think this is for bolt actions as John suggests.
Chuck