Speed Twin Seat Commonality?

I'm going to be getting a Speed Twin in a couple of months. I'm wanting to get a seat custom upholstered for it in the meantime. I intend buying a second hand or damaged seat off ebay or from a breakers to get re-covered.
Can anyone tell me if the Speed Twin seat base (pan?) is common to any other models (Street Twin, T100, T120, Thruxton etc.).
Or, alternatively, if a Speed Twin owner could post a photo of the bottom of their seat, I could maybe identify a matching seat base.

 

Thanks for that. But a part number will only be for a particular model's seat.
That's not to say that the nylon moulded base (on which the vinyl/foam sits) isn't common to numerous models.
I'm getting rid of the vinyl and foam so it doesn't matter what bike it's off (if indeed the ST seat base is common to others).

 

I think I've found the answer. Speed Twin seats aren't interchangeable with any other bikes.