Thinking about piping my 61 FX. Since all the Hatori vendors in my area are mail order I'm curious about some header sizes and pipes.

1. The Hatori #750 and #751 (short radius) headers... I suspect the short one will fit my aeroplane but what exactly is the radius? In mm?

2. Does these fit the OS 61 FX mounting holes as it does the OS 61 SF?

3. What is the difference between the #650 and #668 pipes? The measurements are said to be the same on the websites but the latter is more expensive. How come?

Many thanks for any help.