Thanks to all.
Much as I like the ally ones I have purchased a dual chamber Girling which has a built in level indicator and is SVA compliant and is overkill on the fluid volume. The RCR suggestion would not work as I am fitting a Tilton 900 pedal box
Tilton Engineering - Brake, Pedal Assemblies, Floor Mount.
Onwards and upwards, hoping to be ready for LeMans classic next year
John