I've got 4 in LTM: two from the 60s and two black ones. If mine are anything to go by, I don't think you take a real risk with J-8s. They're all really good for black and white, but only good for a certain look on colour (my experience, anyway). Things to look out for are: With the old silver coloured ones, it probably will need a relube. This really isn't tough to do with the silver ones, and I've found the grub screws to be much more resilient than the later ones. One definite advantage of the silver ones is that only the focusing ring turns, whereas with the black ones it's the whole lens. This can mean too much play against the camera for my taste, and I had to fix this on both of the silver ones.
I have a feeling that the coating on the black ones is a bit more refined - but it's only a feeling. The silver ones are better ergonomically IMHO and look cooler on a black camera; although, you hardly get that 'stealth' effect that some rf shooters go for.
Do watch out for the rear element being loose. Give the lens a little shake and see if anything rattles. If so, it's very easy to tighten, but I had a whole roll of 36 that wasn't totally sharp after a long journey vibrated this loose. Nice lenses to work with: easy to get at all the elements and there's little you can do to instantly turn it into a paperweight.
Cheers,
Richard.