The bulkhead does have some holes like when they get galvanised. I had a look at the FAQs online and the C suffix is shortlived..
1966 C H ?? Front Engine cover no studs water pump (Petrol 4 cyl)
Apr 1966 C D ?? Strengthened layshaft
Apr 1966 C ?? Centre horn push, Steering wheel all
Apr 1967 D J E Negative earth, Rocker brackets, Zenith Carb, Single grommet bell housing, Cranked handbrake (Petrol 4 cyl)
May 1967 D H E Negative earth. Single grommet bell ho
another says:
January 1964 - 'Curved' front apron replaces 'Flat' type.
September 1965 - Chassis suffix 'C', Plastic spoke steering wheel fitted to 88" and 109" models.
September 1965 - Chassis suffix 'C', Narrow type sill panels fitted to 88" and 109" models.
September 1966 - Series 2b Forward Control model introduced.
April 1967 - Chassis suffix 'D', 'Long' type hand brake lever fitted to 88" and 109" models.
April 1967 - Chassis suffix 'D', Vehicles changed to negative earth system.
April 1967 - Chassis suffix 'D', Lucas DR 3A Single type Wiper Motor (Square body) fitted to 88" and 109" models.
April 1967 - Chassis suffix 'D', Front Seat Safety Harness and Anchorage fitted as standard to Home Market models.
May 1967 - 6-cylinder engine fitted to 109" 'Regular' models.
May 1967 - Flat heater introduced.
February 1968 - Chassis number 24131337D, CV type Brake Master Cylinder replaces CB type on 88" models.
I'll have to load a pic.
Looks like I'll need a late suffix workshop book to get a decent diagram.