Thanks, Michael !
In this assembly, I did not use any heat dissipation devices. I applied a simple scheme of sequential actions - initially massive metal parts are welded together and only after that small parts are soldered. In a short time of soldering smaller parts, the remaining larger ones do not have time to heat up very much. Therefore, the parts do not fall apart from overheating.
A special role is played by the composition of the solder: Sn - 50% Pb - 32% Cd - 18%
This solder spreads very quickly in the right direction and this nuance allows you to reduce the heating time of the surrounding parts, protecting them from overheating.
With this soldering, I mainly use a 30W and 60W soldering iron, very rarely 80W. And only the sharp tip of the soldering iron.