For a JTV69,... 3mm on the Low-E side, 2mm on the Hi-E side.
You may still need to listen to it and dial it in. Assuming you're using the stock pick-ups.
Custom pick-ups is trial-and-error. Custom pick-ups,... give me the bulk resistance spec,
and I can make an educated guess.
I enquired at Kinman regarding the oft-still used "resistance as output measurement," and I could feel the smirk behind the very informative explanation denouncing it. It's evidently got less to do with "output", than people would have us believe. Kinman doesn't even use resistance measurements in the public domain, as it's a furphy, particularly when you're talking about pickups that are not made in the "conventional" way. Well maybe Kinmans are still "conventional", compared to piezos into a PCB, and digital modelling, but their construction is certainly far enough away from a simple wire wrapped around a magnet, that meaurements such as these are useless...
Further to these, it's worth noting that Kinmans use magnets with far less "pull", and would be well worth investigating in JTVs, and Standards IMHO.
Here's a relevant extract from the reply email from Kinman:
"So I am very surprised that any manufacturer who know these things would issue advice that talks about suitability of resistance for their product, it's complete non-sense. I think what they are probably driving at is the actual output in millivolts, which indicates the amplitude or strength of the signal in RMS terms. A more general indication of output in mv is a simple loudness comparison. I suspect they are trying to tell you that their electronics don't like high output pickups (excessive number of milivolts, nothing or very little to do with Ohms.
So applying that to Kinman's I'd say to play it safe steer away from the Big-Nine-O, Woodstock and Hendrix sets and the SRV set and the individual pickups that comprise those sets."
For the record, I'm sharing this info to illuminate, not to ruffle anyone's feathers...