Just use nickel wire 1455°C melting point, then silver solder it. I silver soldered the Z gauge rail back together for continuous length. Then fed all the rail back onto the sleepers, that was tedious.
Use hard silver solder 810°C to solder the bottom of vertical pieces and then medium silver solder 775°C for the top joint. Silver soldered joins are really strong, more like a welded join. The solder comes in sheet form and just cut along the edge, almost to the end, with scissors, then zig zag back to the other end so you have the remainder to hold on to, simples!
Heat the join and the solder will flow in. Basically the same as circuit board soldering. After a dozen goes you will get your timing right. Clean off flux residue properly, needle files are handy.
Make up a jig to hold everything in place. A well designed jig/s is the key to soldering easily, might be a few iterations of design. With a proper torch with fine point, not some cheap disposable pack. Spend the money on quality tools to make the job easier.
Vertical piece of wire maybe better to do longer and then cut off. Same goes for the horizontal, wasting some length will probably be easier to fabricate. The weight of an old chisel might do the trick holding down the verticals on the horizontal section.
You will get solder & flux from a silversmiths jewelry supplies, and some needle files will be handy plus good quality end cutters. Flame proof board so you don't burn things (in the old days it was asbestos).
The hardest part here was getting the two pieces perfectly aligned. My first jig was more complex with adjustment screws to push the rail into position on X and Y directions. I over thought the jig and with thermal expansion the jig backfired.
(a slight gap at the ends simply for the photo, the tighter the join the better for structural integrity).
Depending on how you design your jig, you may need to allow for thermal expansion, so a spring may be required to maintain tension, but I think I am over thinking a jig!
Once you get going and practise a few stuff-ups, more to the point get your jigs working properly, silver soldering is quite therapeutic. You will enjoy it.
Last but not least, good soft area lighting and a dark background for good contrast to see the detail of the job easily.
