I used a 100W soldering iron that is quite powerfull (10mm soldering tip) when i did this on my 56.
Solder that I use for doing the electonics worked quite well but the thing needs to be heated which req. a lot of heat energy. With a massive tip this energy is already saved in the tip. Make sure you sanded all parts before soldering. I pre-soldered the arm and the carb first (keep the hole). I installed the whole thing together with a little scew and soldered it while screwing it together.

Btw: good engine choice...
My is now turning 7100+ on a 22x10 3Blade Engel Prop (@sea level) using two tuned pipes.... >16kg thrust in a 8kg Ultimate -> nice
Forget about the MVVS 58 or the DA50 ;-)