First, play the pos pickup, so you know what it sounds like, then swap mags and notice what changes. That tells you a bit about what a different flavor of mag can do.
Did you read the page Tone Fiddler posted? The 59s were reportedly based on Jeff Beck's 59 Les Paul. They switched to A5 for lighter string gauges (though that sounds dubious to me; I'd expect A5 just worked with more modern music demands.). But anyway, the 59s weren't originally A5, and they take mag swaps very well. Most every mag combination people have tried worked for various kinds of music and versatility.
A 59 can't be made to sound like a Seth Lover with just a mag swap. Just like putting an A5 in an A2P makes a Jazz, not a 59 model. Different coils sound different. The mag just tilts the frequency response of that particular coil combo.
I'm aware that the wind, screws, baseplate, etc. will have an effect as well as the other parts.
I just thought it would sound close enough to a Seth to not be worth the trouble of a mag swap when you can just get a Seth. And I also thought the 59 wind was in the ballpark and just needed help from an A2 to sound more vintage.
I would have assumed the first candidate for the A2P would have been a 59 before a Jazz since some people say a 59 sounds warmer and thicker than a Jazz. I don't remember the 59 sticking out in my mind in any way when I tried it out, which is why I thought an A2 might make it better.
9s and 10s have been the most common string gauges for standard tuning for decades. That's why the thing about the strings being too light--even in the 70s--seems odd to me.
Plus there's rough vs. smooth vs. polished magnets, oriented vs. unoriented, who makes the magnet, all the other components in the pickup. It's just more trouble than I care to mess with, especially when there are already so many preexisting pickup models out there that might sound largely the same wo me having to do the work myself. I feel like by customizing the pickup too much I might as well just be building my own.
Regarding a "pos" pickup, since tone is largely about taste, I doubt the quality is that much worse than a US made pickup. Rather, it is probably less shielded than a US made pickup, and it probably has two conductors instead of four. It might sound slightly harsh or muddy but some people may be fine with that.
The effect of the winding of the pos pickup, I think, would be difficult for me to separate from the effect of the magnet. And even if I practiced on a pos Acme pickup (thank you
Clint 55 for putting "pos pickup" in my vocabulary
), there would still be the stressful first install on a name brand pickup.
And I also know largely what I want by now. It's mostly just trying stuff for the sake of trying it. I never knew EMGs could be improved upon until I heard Blackouts.
These days I tend to prefer Alnico V type PAF sounds of moderate output (say 12-15k) for rhythm sounds because of their clarity. Ceramics of a hotter variety get solos and melody work. A2s of a low to medium output usually get the neck position unless I want a bright JC120 type bright clean sound from the neck. Then I might go with something different.
I think I've posted this before but in my experience a Custom 5/Custom with Triple Shots is the most versatile pickup combo I've ever tried. It's the only time I can get a warm and a bright clean out of the same neck pickup, especially if I run it in parallel out of phase.
