Rectilinear 3's: Is it worth upgrading tweeters???

Does anyone remember the Rectilinear 3's??. It was a floor standing speaker considered almost hi-end in the early 1970's. I ask, because a friend has inherited a pair in very good condition, but has no interest in them; so, I may buy them because they are audio "classics" They sound very good for a 30 year old speaker but are also a little slow, and imaging is just average. Anyone possibly have a pair of these speakers in use in their system?? I would like to hear from you, especially if you know of any "upgrades" available that can be made to improve the imaging, but still perserve the speaker's neutral sound character. Thank you, SJ