[64 SPLIT]

Welcome to the forum! Looks like a great van you've got! 👍
Really like those seats. Looks pretty similar to my van with the Caravelle rail conversion in the back too, provides a really flexible layout.
You could get the Caravelle full-width bench seat for the rear which drops down in to a bed (have it in my van) and then you can either use a Multiflex bed extension board (or make your own), or fold the single seats to extend the bed.

 

[64 SPLIT]

If you need any measurements for the rear triple just give me a shout - the Caravelle's lose a lot of space down each side due the plastic trim panels.
Looking at your rear speaker pods, it definitely wouldn't be able to slide all the way to the back, but it would be fine further forwards and allow you to use a multiflex board / legs to make a bed from.