Hi guys I am going to by this barrel for my 1894.

http://www.gunpartscorp.com/ad/882400.htm

I called numrich and they say its ready to go, just needs switching. Has the thread and chamber cut, as well as dovetails.

Obviously a barrel vice and an action wrench.

What about go and no go gauges, will the timing work out for all Winchester 1894 rifles are all slightly unique?

I am just concerned with head spacing and having it threaded to the correct point. My concerns may or may not be justified, I know nothing on this subject.

I have two friends who have changed barrels before, one said he could do it no big deal, the other that if the timing is wrong, you may have to take a touch off or shim it and if its a mile off rework the thread and cut a new chamber, requiring a chamber cutter. Which one of them is right?

Barrel vise. You already have a barrel vice or you wouldn't be posting here.
And the "action wrench" is a big crescent wrench. 94 barrels are not on tight at all.
Both of your fruends are right; but note that the second guy said "IF...". Which is true.
I have not used one of these barrels but I assume they timed the threads and chamber rim depth. Headspace on these can be, and often is, generous and presents no problems on these low pressure cartridges. So they should be made to crank right on and shoot. Get one, and then tell me what happens when you try to install it. I can fix it if it does not fit. Oh, I see you are down under. That might be a problem.

So really it comes down to luck, and how precisely the barrel has been machined to suit the action of an 1894?

Hopefully it has been machined to time correctly, its not an expensive barrel!

On pre-64 Model 94's the timing will usually be correct. The same is true of Model 70's and 54's. On post-64 models, it's a crapshoot. Regards, Bill.

Yes, it all comes down to how precisely the barrel was made. Only way to find out is to try it.