I called in at Lifes' a couple of months ago (v. friendly and make a nice cup of tea) and they mentioned this option as I'm 6' 5". They then phoned another dealer (cannot recall which) who said its no longer possible or rather today's Morgans already in effect have the benefit of recessed saddle seating.

That said it does seem possible to liberate more legroom in 4-seaters as I've sat in one (sold by Allon White 6 - 9 months ago) where the plastic cover over the rear leaf springs had been removed and the seat runners moved backwards allowing the front seat to slide back on to the rear seats. If that's possible I don't see why the rear bulkhead in a 2-seater couldn't be moved back a little more assuming the battery is accommodated under the bonnet.

Let me know if you find out more.