Unusual Dickson toolpost with dovetail?

[sploo]

Wondering if anyone could shed some light on this rather unusual toolpost? It has two Dickson type tool holders, but the wheel on the top controls a screw that slides the body along dovetails slots. If it's for a lathe that would surely be a bit pointless (given that metalworking lathes have slides). Anyone know what it was intended for?

 

[Sideways]

I could picture this block being being fitted directly to a lathe cross slide instead of the compound slide. In that application, the dial would act as a fine adjust to replicate the function of the compound slide for limited applications.
The advantage of replacing the compound slide might be lower cost, greater rigidity, ?

The thing prompting the idea is that the bottom of the compound slide on my old 1950 Harrison looks like the bottom of this block. The only difference being mine fixes with 2 bolts, not the three (holes for bolts) around the circular boss on this.

 

[TFrench]

I can see it being use useful for internal threading jobs as a quick retract - you could leave the leadscrew engaged like on a hardinge and just bring the tool in and out on the toolpost.