Soldering and body leading aluminium.

[Olds]

Yep, sounds wrong doesn't it.
In preparation for fitting the body on the speedster, I've been playing around with some sticks of Alu-Build 300 which is fine except that the sticks are fairly expensive, the finish isn't that great and it's harder than the base aluminium, so you certainly wouldn't want to use it to fill dents etc. and while it supposedly works on brass, copper and zinc alloys, it wont ever adhere to steel.
 Did find while messing about, in an effort to find a more economical way of using it, that if you use this stuff to 'tin' the aluminium, then normal lead solders etc. will happily bond to this. Not tried lead free solder yet but I expect the result to be the same.
  Take this one stage further and suddenly you can cheaply solder steel to aluminium.

This may be old news to some but I had never come across this before.

Steel screw soldered to aluminium (plus curious puddy tat).
And after fatigue cracking the aluminium by holding it in a vice and working the screw back and forth, also hammering it. Seems to be quite well attached.

[the coppersmith]

Alchemy. That's very clever. I seem to remember being told that lead solder is far better/stronger then lead free solder in the way it shears and bends. However with all this about poisoning with lead pipes etc. lead free has become the norm. I recently had to alter some bus bar for a small company and they insisted on using lead solder for better conductivity as well.  They have had problems with lead free solder used in this way. I will now have to join in your experiments and try different alloys etc.

[Olds]

I still have some old reels of lead solder plus some leading sticks. I also came across a couple of old lead sash window weights, so I should have enough to last a while. Just need to source some tin.