I've brazed all kinds of stuff before. Just as long as you remove any rust and dirt, and heat steel up until it's glowing red and a little glossy, you can braze pretty much anything. One time, with careful heating, I bridged about a half inch gap between 2 pieces of steel. That wouldn't be practical, but I did it just to see if it could be done. So, tolerances aren't that important. As long as the gap isn't over 1/8inch, it shouldn't be any trouble at all. And if you do have some, just tin the edges of both pieces, and then add filler with them set next to each other.
There was a piece of brass tubing lying around one day, so I cut off an inch or so, notched the big pieces end, and welded the piece I cut onto it like an end cap. It welded together much like aluminum. And I did get a water tight seal, incase any of you were wondering.
