It was indeed the DC-4 at Frankfurt. I've just checked the "Deaths Overseas" index on line to find a Peter A Gutteridge, aged 26, registered as a death in 1967. As a clincher, and an interesting insight into bureaucracy, the "Location" in the index is listed as "Civil Air".
I suppose he'd have been a retired senior captain by now - che sera sera - RIP Peter and many thanks to all who have contributed in just less than 12 hours. Well done AH & N.....