I think the thing is , Bob, that anything is better than the standard manifold. I once spent a lot of time calculating pipe lengths and came to the opinion that the 27 inches as recommended by a well known seven tuner before I enlisted the computing facilities of one of the worlds largest aerospace companies, ( they didn’t exactly know about it) was about ok. In fact any multiple of this will do, so if those pipes look about 13.5 inches, then that will do. Agree about pipe diameter though.
Alan Fairless