That's superb, and a very tasteful build too.
I believe Reynolds 653 is very similar in its dynamic characteristics to 853, isn't it? But Reynolds had to develop 853 because 653 can't be TIG-welded, as it can only withstand the lower temperatures involved with brazing. I must say I'm surprised the bike is so light, but the tubes look very skinny, perhaps all of them 28.6. And as others have said, the confidence to show off the brazing under the clear powdercoat is a very nice touch indeed.
I think it's also very clever for a hand builder to be able to design a full-suspension frame so well, but to be realistic I guess the design must have been preempted to a large extent by adopting the AMP rear end, mustn't it? The AMP must surely dictate that the pivot point be exactly where it is, which would take some of the more difficult theorising out of the equation. But even so, it's impressive for any year, let alone as early as 1993.