Best cartridge for very old worn vinyl

Howard, good for you! It just goes to show that following the manufacturers recommendation usually pays off, especially with cartridges by the same manufacturer that were specifically meant to be used in this particular arm. Ikeda certainly knew what he was doing. The FR7 and FR64/66 were made for each other and the sonic results speak for themselves.

Ikeda was very consistent in observing the 51mm collar to tip distance. I have 4 different ones (including the MC702) and they're all exactly the same. Ortofon is slightly less meticulous with the SPU and I've noticed up to 1mm deviation in some cases. Not that I can hear it! 

Other integrated headshell cartridges may use a different distance. Some are adjustable, like the Dynavector DV-30 series. Some are not, like the Sony XL44/55 Pro serie. The Sony has a 49mm collar to tip distance to accomodate the proprietary geometry of the Sony arm (neither Baerwald nor Stevenson). But in the manual they explain that even this 2mm deviation from the SPU 51mm norm is still acceptable and will not be audible. I kind of doubt that, but go figure!

But now for the million dollar question: do those Argo's still have groove distortion with the correctly aligned FR7? Curious minds want to know.....

#edgewear, hi again !
In the end I went down a slightly different path and bought a SMARTtractor as I’m a big admirer of Acoustical Systems work in analogue.
I spent some time setting up my favourite FR7 (fc) and other “conventional” cartridges (as precisely as my ageing eyes and paesano fingers allowed) to the UNI DIN curve exclusive to that device, rationale  being that this is specifically aimed at the 1960s Decca vinyl I tend to listen to (and hence the raison d’etre of this thread !)
The results were amazing - I ran all my newly aligned cartridges through a particularly nasty early Argo pressing of a choral service at Westminster Abbey. I suspect that even when totally new it would challenge any decent cartridge let alone the agricultural crap that no doubt ploughed through it for the 50+ years before I got hold of it...
Result: everything sounded good, every cartridge (from Denon 103r to Koetsu Jade d/c) produced texture where there had been glass and tamed all but the most extreme garbage caused by damaged vinyl (nothing on earth can surely repair vinyl ...).
All in all this was the solution I was seeking when I posed the title to this thread. Now I have realigned as above, all of the cartridges realigned now do a good job of playing early Argo worn vinyl. Some are better than others but that’s the same difference I get on pristine vinyl.
This may not be conforming to everybody’s way of doing things, but for me, in my system , it’s worked very well indeed...:)

@Howard, good to hear you found a method that works for you. Dieter Brakemeier of Acoustical Systems used to be one of the experts who strongly advised to change the P2S distance of the FR64/66 to facilitate the use of the Baerwald geometry (you can search this forum for his contributions under the moniker dertonarm). Apparently he has now created his own UNI DIN curve, probably a refinement of the Baerwald. Judging from your enthousiasm I might give this geometry a try, as I also have many of those 60's Decca's. Thanks for sharing your experience.

None!!