Just make them fit around everything..... If we were 1:1 the length of the tubes / ID of the tube / air flow into engine/heads /class rules for exit......and so on. If you are doing an exact class or car get reference photos off Google or the web. The biggest trick with using solder is getting it flat...roll it between sheets of glass or plexiglass, then polish and bend. In this '31 the tubes are equal, and bent to shape then the collectors were added.