I just measured a 450 head for you - it is about 5-1/2" - but then so is a 350 (and probably others as well).View attachment 228690 I am trying to figure out what this pipe fits. It can out of a old honda dealer. It measures about 5 1/2" from center to center.
You may be right - aftermarket for 360...I see what you mean, they look a little too splayed out to me. I'd guess they're for a cb360.