The 52t and 39t chainrings on my Ultegra FC-6603 triple are getting near to needing replacement. The 30t inner is little-used so far, so plenty of life left in that. And in any case, the chainset is being repurposed onto a loaded-touring bike, so I'll be fitting a 26t or 24t TA inner at certain times too (i've seen reports that 52-39-24t works fine on FC-6603 and with FD-6703 or FD-6603 front derailleurs - not sure about with 105 FD-5703 though, which has slightly lower capacity than the two Ultegras).
Of course, as noted here already, 6603 chainrings are no longer available. Fortunately I have 3 x 39t 6603 unused middles in my spares department.
However, for spare outers, I only have chainrings specified for double chainsets in my NOS department - 1 x 6600 52t and 1 x Dura-Ace 7800 52t.
I'd have thought these double outers will work just as well as the original 6603 52t triple outer - I mean, how different are 6600 and 6603 in 52t likely to be in use? And likewise, the 7800 52t should work as a decent replacement for either.
Unless there's some weird teeth offset or spacing or thickness difference between Shimano double and triple outers of this vintage.....but initial inspection suggests there isn't. And I can't imagine that differences in ramp locations would amount to much practical variance in quality of shifting performance from 39t to 52t in either double or triple configuration/setup/design.
I am going to go ahead and try the double 52t as the triple outer anyway, but has anyone already got any direct experience?
Also, does anyone have direct experience of how different in practice FD-5703 and FD-6703 are when it comes to exceeding Shimano's usual conservative stated capacity limits (20t and 22t respectively)? When I fit the 24t inner, as several people have done successfully, the front difference will be 28t.....
