Standard seats, roll cage and six point harnesses

[gm44]

I currently have the normal leather seats in my 2017 Caterham and am about to fit an academy roll cage.  I'd appreciate advice on two questions:

- Does anyone know of an alternative seat base that would allow the use of a six-point harness with the standard seat frame, back and head rest?  It's only for track use so I'm not too fussed about appearances.

- Can a standard seat be removed with an academy cage in place?

Thank you Gerard