https://www.audioheritage.org/vbulle...6&d=1144944024
I would simply replace the capacitors with more modern parts.
These jbl networks have inductors with specific dcr. The dcr is an important criteria for the crossover filters to work correctly. It’s best left alone unless you have the original factory parts lists.
They generally used Mylar capacitors in that era. Any metalized polypropylene capacitor is going to offer more transparency. The Mylar capacitors sound like a pillow over the loudspeaker.
If your interested in the charge coupled Solen Fast Cap crossover upgrade l suggest to keep the original crossover and mounting the Solen capacitors on a separate piece of plywood.
The values will be 27uF x 2, 8uF x 2, 3uF x2. The 1/4 watt 2.2 meg ohm resistor should be also hot melt glued to the board. The battery can be mounted with a 9 volt battery holder on the plywood board. Simply remove the existing capacitors from the stock crossover and run flying leads to the charge coupled capacitors. Depending on the rest of your system there should a noticeable improvement in transient detail and transparency overall.