Thanks Martin, yes the chrome bases are Hunter/Reliant/Aston Martin for Lucas L782. My original Commer ones were black plastic bases for L782 and had the separate indicator and stop lenses to match - rather than these one piece versions.
My van was first registered in April 1975, so that would've been it's first licence - although I've used artist licence on where I was living at the time (aged 5 years !). With everything now all online plus £0 as in historic category, that custom repro tax disc cost will be all I have to ever pay