I used to sell them both. The 107 is a much better speaker as far as I am concerned. It was about 3X the price of the 104/2 and was the TOTL. Stereophile listed the 107 as one of the most significant speaker designs ever. The 107 need the KUBE to perform properly as it was designed into the system. The 104/2 was designed before the KUBE was developed so they are fine without it though adding the correct one will extend the bass response.
The 107 is more of the classic Kef sound, the 104/2 was made to appeal to North American consumers and is a bit more upfront and forward sounding. We did have some customers who preferred the 104/2 but the best thing is to listen for yourself.
By this time both may need some attention as they had foam donuts around the voice coils (both models) and foam surrounds (all 107, later 104/2) that are likely rotted out by now if they have not already been changed. The Ferro fluid in the tweeters tends to dry out and should probably be replaced though I have not done so on my 107s.
Good luck and let us know how it works out!