Thanks, got it - now a bit of mental positioning...no doubt the artist had been there himself in person, that inner Trilithon is just perfection. The uprights behind the vandal and his mate [either a fisherman bragging about the one that got away, or his wife telling him about her first husband!!] are sketchy at best, but the angles are all wrong. A single position at the open end of the horseshoe looking East-ish would give a right-ended lintel end, but the lintels would then be complete on the left side, which they are not in the etching. Further into the horsehoe looking round 57 and 58 towards the only single-lintelled stones [21 and 22] would mean that the stones surrounding 16 were still standing at the time. The end lintel is the clue, but something is wrong somwehere. Was there not an empty socket found in front of the current Altar stone?