This is the relevant extract:
They called in two artists, Charles Raymond and Chris Foss, explained what they had in mind, and showed them Comfort's own rudimentary drawings ("Alex was suggesting things we'd never seen before," claimed one) and some explicit Polaroids of his sex life with Jane.
Raymond and Foss still were not sure of the best way to present to the thunder-struck British public 200 illustrations of a man and a woman having full-frontal sex. They looked through soft-porn magazines in search of inspiration. They hired models from Soho for their unique perspective on sexual activity. Then Charles Raymond had a brainwave. Why didn't he demonstrate 100-odd sex positions with his German wife, Edeltraud, while his friend Chris photographed them, and then both men could produce line drawings from the resulting snaps? Edeltraud was enthusiastic, bossy and efficient. "Charles!" she would say, "Position number one. Come on, Charles!" Then she would tick off the number on a piece of paper and say, "Right Charles, now we do this one . . ."
Mr and Mrs Raymond are, therefore, the couple - the hairy caveman and the stroppy fraulein - that you see in the original book, drawn faithfully by Raymond's own hand and that of Chris Foss.