I don't have any much older than around 1970 but the ones I do have are still putting out just fine, the OEM lights leave a bit to be desired. I am currently running a 1973 AG hub on my Twenty with a B&M Retro headlight and a Spanninga LED tail light, other than the fact it is a 2.4watt versus the 3 watt of the front hub dynos it does the job.
Aaron