Best cartridge for very old worn vinyl

@Edgewear, many thanks !
I’ve figured out how to move the FR66 tonearm in the Balance, so I obviously couldn’t resist having a play around.
With the FR7fc in the arm I moved the arm pod around until the tip of the FR7 stylus  was lined up in the single “bullseye” on the Brinkman alignment tool. Previously the FR7 and SPU carts I own all sat a few millimetres short of this point, whereas all my non-fixed headshell carts had been adjusted to this alignment.
In other words the FR7 was now aligned the same as all my other non-fixed headshell carts (for the first time since I owned them).
To cut to the chase the improvement in sound quality was quite astonishing, way beyond any confirmation bias or other mystical bs to which I am prone.
What I still struggle to understand is why two cartridges, aligned identically, don’t obey the same laws of physics because they are made by different manufacturers. I appreciate that an SPU comes in a fixed headshell so you need to adjust the arm to align it, but once you have done so then it is no more or less aligned than a cartridge that can be aligned in the headshell itself (because it’s not a fixed design).
Without understanding the science one iota I do know that people debate which alignment method is best and I also appreciate that Ikeda seemingly used the Steveson alignment when designing the FR tonearms but does that mean that any cartridge mounted in an FR tonearm is misaligned unless it’s been set up to Steveson alignment ?
Again, I fully understand that ultimately one of these alignment “philosophies” might be better than the others, however isn’t that something that would then apply to all arms and all cartridges given that they are presumably based upon the laws of physics rather than something in the actual tonearms and cartridges themselves ?

Howard, can you measure the P2S distance of the new position you found for the tonearm? According to the FR66 manual the mounting (or P2S) distance should be set at 295mm. Only then will the FR7 be correctly aligned to Stevenson geometry.

You mention that the FR7 and SPU came several mm's short on hitting the 'bull eye' at the previous dealer's position. This seems to indicate that the P2S distance has become slightly shorter in the new position you found. Correct?

If you prefer to keep the arm mounted at this new P2S distance you will need to reposition all your other cartridges, otherwise they will now be misaligned. Basically it means all cartridges should have a headshell collar to stylus tip distance of 51mm, same as FR7 and SPU.

FR7fc has a conical tip and this tip profile is less sensitive to the adjustment, this is the one and only benefit of a conical tip :) When all other profiles are a bit off the alignment, it will be irrelevant for a conical tip.

If one of your FR7 has longer cantilever than others then one of them is probably not the original (but a re-cantilevered version). Because they are all designed for FR tonearms first and you know PS of the FR arms. When FR cartridge is off with correct PS on FR arm then it is a bad sign (the cartridge has fake cantilever). You’d better check everything again slowly to make sure.

When you align any cartridge with one point protractor then you have to alight the cantilever, not only stylus tip position. You can reach the point with your stylus, but a cantilever and the hole cartridge will be certain degree off the lines. If you will change PS distance to reach the required point with the stylus then you will notice another problem soon, the problem is that a cartridge position (and cantilever position) is not parallel to the lines on protractor. You can fix it only with conventional cartridge on conventional headshell with slots.

@edgewear, hi again, I measured the s2p of the FR66 in the “new” position (ie the position of the tonearm whereby the stylus tip of an FR7fc sits in the “bullseye’ of the Brinkman alignment tool) - and its 295 mm (!).
Most definitely the FR7fc and SPU synergy both sound much (extremely) better in this position, in fact I venture to say better than anything I’ve heard in my system to date (including the cartridges that were each aligned in their headshells such as Koetsu Jade/Vermillion and London Reference (Decca).
I’m going to follow @Chaksters good advice about the Feicker protractor in any event but this is getting quite interesting as I wasn’t expecting such a jump in performance with the fixed headshell carts.
One issue I may face is that the other cartridges will all need to be moved back in their headshells and I’m a bit concerned as to whether there will be enough adjustment possible there as might be needed. I’ll cross that bridge when I come to it !

@chakster , thanks again.
i understand the point that fixed headshell cartridges can’t be adjusted for zenith (or azimuth). so how is this solved on the Feickert alignment tool ?
cheers