No bobbins in my type 54, just holes with fender washers.
I would like to suggest that you dry fit the new seats to the location that you like and drill holes based on that location. There is enough variation of interior (carpet and such) and the seats themselves that 3rd party measurements may not align with your car.
I am working that area, as we speak, on my car. I found stress cracks around some of the bolt holes. I re-inforced that area with about 3 layers of new glass (tapered edges to distribute the stress) to repair and prevent.
Ron