Very interesting that, at least on Novarossi's pipes, you can use the same pipe with different headers to obtain different behaviors. Which make sense since, as you said, the length of the entire system is important, not only the length of the pipe.

"This is the Novarossi 9853 'Super Strong' polished racing pipe (no manifold). This is the one piece variety and requires an off-road manifold, which attaches to the tuned pipe using three small springs (not included). This pipe is designed for excellent bottom end/mid range performance and is a great pipe to bring the bottom end to life on Novarossi 421B engines. This pipe is an excellent choice for any engine that works well with a 053 pipe. The 41005 header is an excellent choice for this pipe for strong bottom end power delivery, while the 41001 header is recommended for better mid-range/top end performance."