I fly rather large models on a regular basis. The 14 lb B-29 that I fly uses this 4" bellcrank with .027 leadout braided wire with .024 diameter flying lines. I also have a 12 lb sport model that is used as a camera platform. I have a flown a 20 lb model (1/3 scale Spacewalker) and a 17 lb 1/4 scale Morrisey Bravo.
The larger models fly better because the wing loading can be higher than with a smaller model.
https://brodak.com/brodak-6.htmlDo yourself a favor and install an adjustable leadout guide. Typically one installs one of these for trimming with aerobatic models but in this case we are going to adjust to keep the line tension within reason.
The larger models pull more. When I fly my smaller models like my 3.5 lb spitfire it pulls but nothing like the B-29.
A special Heavy Duty bellcrank is not required.
Fred