412USA,
I have two sets of 406 front discs fitted to my two 400s , one with Alloy Coopercraft 4 piston calipers, the other with Girling #17 cast iron Calipers.
Both work well compared to the standard drum brakes . A great safety feature driving a speed keeping up with today's traffic
Measurements of the 406 front Disc compared to a used/worn Britannia front disc
406 OD 11.25 inch , Britannia 10.875 inch
406 Offset 34mm , Britannia 28mm
406 thickness 13mm , Britannia estimated 13mm
Overall height when laid flat 406 47mm, Britannia 41mm
Brake Disc Rotors are available ex BG Developments/Bromsgrove UK
HOME
406 Front BGD3993
406 Rear BGD4197
407 Front BGSD 121-10
409 Front BGSD 136-11B
411 Front BGSD 50-10
411 Rear BGSD 50-11
As you can see all the listed discs must have different dimensions .
I hope this helps .
Geoff