Have you considered the low temperature aluminium welding rods?.........it only needs a propane torch to do the weld and is machinable afterwards although I would manually finish a weld if the machine is in one piece and not stripped down.
Using those rods it is important to get the base metal up to temperature first and NOT the welding rod or it will just end up as a pile of blobs lying on the surface.
I have a plasma welder and have repaired cast iron with mild steel rods as the resulting cast iron/steel alloy weldment is easily hand worked etc.
Ian.