I haven't any KEF104ab's of my own, but I have heard them, and liked them. I also built the crossovers, and used them into KEF B110 and T27. The 'extra' bits in the crossover network meant that the roll offs of the two units became more like modelling suggested, especially outside of the crossover region. I remember getting very close to the two units just mounted on a small baffle (part of a larger one) and not being able to say where the sounds were coming from, so good was the crossover. It may be worth upgrading your capacitors from those dubious quality bipolars, which, by now, may be showing their age!
Good luck. [don't worry about upsetting the odd fellow (or two) there will always be someone to back up your side of things.
] Giving incorrect info, especially for valve circuitry, could be dangerous, so we have to be vigilant.
Lenco 59, Rega 250 + s/s stub and c/w, cAT92e cart in a metal housing, Plattermat mat, Michell's clamp,
Musical Fidelity X-LPSv3, Cambridge Audio 640v2 x2
Usher 604 floor standers augmented with Fountek CD3 ribbon tweeters