The diopter value should be the same, because that's set by the screen, and your eyes.
I'm not sure if a 'WLF' diopter will fit all vintages of finder. Mine is from the '80s so I don't have that worry. You might try asking at photo.net where a number of ridiculously well-informed Hasselblad junkies still hang out in the tattered remnants of the medium format digest.
MXV in the UK have a number of WLF diopters of various strenghts at very reasonable prices, so it wouldn't cost too much to try one out. They are good to do business with. www.mxv.co.uk.
I don't know if the lens in the old-style could be exchanged by the user. It has been a very long time since I looked through one. But even if it was, and I think it's not, you would have a very hard time finding the right diopter. For the later wl-finder which is pulled open on a plastic tab diopters are readily available. You could as well get yourself a chimney finder with is adjustable, has an undistorted view but a bit less magnification but, on the downside, can't be folded.
I was able to find another newer WLF, which has the round diopter. Well, it was no better in terms of eye relief and basically the same thing in a different package. Next up: chimney finder.