Thanks for the replies. The reference I've seen to a "crew rest position" is in an official document (circa 1951) referring to the conversion of a UK Lincoln B Mk 2 for special duties. The position was apparently sacrificed to accomodate some kit. A second reference (that I've just come across) talks about the removal of the "rest seat". So I've no doubt the position originally existed in B Mk 2s. Of course, it may have been removed from even standard aircraft at some later date. I've found an illustration showing a seat against the (rear of the?) front spar, next to a fold-up step, which might be the article in question, but it would be nice to confirm.