While I haven't built up my PNG drop bottom gon yet, measuring the frame and comparing it to the 3FCM model would indicate about 20-3/4" coupler-center to coupler-center. I was interested/surprised to note that my Don Winters drop bottom is about 3/4" longer...never noticed that against the 3FCM model before. Phil spent a lot of effort getting this right, so I'd bet on his length being correct.