Mmm, i should have said i also have a van bodied truck, with bulkhead, and oddly i manage fine in that, the thing with the truck cab is the rear wondow section, which stops the seat going back quite as far as in the van. and re the headrest, even with the headrest fitted, my head would miss it totally, so don;t really see much point in having it, esp as it restricts further the seat movement....
I tried mudrails in the van for an extra bit of room, but ended up fitting rover 214sei seats, which suit me fine in the van, but simply don't fit in the truck cab.......
might have to try mudrails again!