I have Altec 604E since 2005.
Two year ago, I built crossovers based on original n1500 schematics using good quality modern parts. The difference in sound is huge. It is like different, much more expensive speakers.
The chokes in the original crossover are OK. But capacitors and variable resistors must be replaced.
I used Duneland Cust resistors and mix of different capacitors:
Jensen PIO aluminum 1.5+1.5uF => 3uf, Jupiter VT 8uF + Duelund RS 4uF+ Auricap XO 2uF => 14uF, Duelund bypass Cu-Sn (3uF) and Silver (14uf), Soviet K71-7 polystyrene bypass for both (3 and 14uF).