CTO

[Don Mills]

Perhaps:
Combined Transport Operator (CTO) is a logistics service provider that specializes in coordinating and managing the transportation of goods using multiple modes of transport.

[John Davis]

Given the Stock book specifications, sounds like a dedicated competition gun. So something like John’s “configure to order” seems plausible.

[Scott Gentry]

Thanks all, Configured To Order does seem very likely the meaning. Lovely gun that was completely redone by Turnbulls before I became the caretaker.