I believe those early L100s with vertical-in-line drivers have second-order highpass filters on the mids and tweets:
http://manuals.harman.com/JBL/HOM/Technical Sheet/L100 CENTURY ts.pdf
They are not rare, particularly, but they are considered by some as more desirable than the later variants with clustered drivers which were produced in substantially higher quantities, and for good reason.
Inspection through the woofer opening with a hand mirror will reveal if there are inductors on the crossover board. If so, your assumption regarding leaving the originals intact and just substituting two caps is invalid. In any case, you'll want operational L-pads also to adjust their output levels.
The LE20-1 tweeters are mounted with three small wood screws which are under the thin aluminum trim ring on the face, which is glued on. It is possible to remove that intact without creasing it with the judicious application of heat and a thin blade. I use several utility knife blades to accomplish it, but there are other options such as fishing line.
To get the crossover out, you will likely have to deal with the same issue with respect to the foil label, as on some variants, at least, some of the screws mounting the board are under it. The mirror will show you how the board is attached to the inside of the baffle and where.
Finally, I suggest that you're not going to "sweeten" the sound via the means you propose if the caps appear to be intact upon inspection and the drivers are presently functioning properly. Despite their appearance, they are quality construction.... :yes:
