The roof mounted trolley pole pivot and cradle is just about finished, awaiting only some M1 nuts to assemble.
It is (or, will be), hinged as the prototype and held in tension by two spring assemblies.
Both a turnbuckle arrangement at the front of each spring ssembly, and adjustable nuts at the rear, will allow control over the degree of tension. The pole will however be held to a maximum elevation by a hook and chain visible in the first picture.
All of this is based on an attempt to interpret the various photographs I have; it is almost certainly no more than a 'representative impression' of the later set up, but should at least mimic the original's flexibility.
The coil springs by the way, were sourced from Springmasters Ltd. Superb selection and next day service.
The pole's top end features a grooved wheel assembly. The various photos suggest at least three different arrangements, one of which looks more like a skate than a wheel.
However, the internet turned up a period advertisement showing Robert W Blackwell trolley apparatus
so another 'representative' component was assembled.
The whole pole assembly will be purely cosmetic and the pole can be removed from the roof cradle for transport etc.