Kombi seats don’t slide, if that’s what you’re thinking.
A Caravelle only has one row of passenger seating (like the California and the Kombi) whereas the Shuttle has two (NB: You can buy single passenger captains seats for the Caravelle for a second row - as they would be easier to remove I presume you’re not talking about these).
It sounds like you want the
Caravelle triple seat or the rarer
California Beach full-width seat/bed. Both work on rails.
Colin at Oxford T5 fits these regularly and is happy to answer any questions you have - he certainly helped me when I was fitting my Cali bed (which Kernow supplied).