fitting a Captain's seat to a Swift Suntor (1999)

[tinsoldier66]

I'm looking for advice on what "conversion turntable" would be suitable to replace the fixed seat in my Swift Suntor 510 (1999).

The ones I've seen online are flat turntables with all the fixing holes on the top, but in my van, two of the fixing screws are at the front of the current metal base.

Thanks in Advance.