If you like the sound of the 4628B, then why not leave it as it is now?
You surely you could lead to a more hifi and refined sound with an active crossover and measurement gears (even with the same drivers complement), but maybe you will miss that old ciname sound that you like.
Why not just add some subbwoofers (spread across the room, not under the 4628's) to augment the bass and call it done?
Concerning the 2404, I think it is the '-1' variant in this model (but then it seems there are plenty of variants there also...). And it better be: the 3khz crossover point would be really low for a 2405 diaphragm. The only way to be sure would be to open it and check the diaphragm width.
If you insist on going active, and you are ready to do -lots of- measurements, I think the best two options are to add a horn on top to turn it into 4 way (a 2370 would do, but a 2397 would sure be cooler), or to replace the 2404 by a
2407.
But then if you ultimately manage to get something as good as a 4348, you will be disappointed as you will miss that 80's sound