76 Ripper Needs Some Work - Leveling, Jack

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I am evaluating a 1976 Gibson Ripper ( to trade for my 84 Martin Acoustic) that is fretless and buzzes around the usual spots (5th and 7th frets).

The ebony fretboard with the strings off has troughs in the fretboard. Have read posts on leveling. Can most fretboards be repaired this way or do they need replacing?

What are typical costs for leveling? Replacement?

If replacement is required can the fretboard be extended adding another couple of pitches?

The other issue is the input jack that was placed on the pickguard and was vulnerable to cracking the thin plastic.
This guitar's jack is hanging on by a thread. Was thinking about asking a luthier to port a hole in the body and putting in a regular jack. No biggie, right?

Finally, the humbuckers are intact and there is a four-way chicken head switch to phase them, etc. Was thinking about two options:
1. Add a piezo pickup/bridge (with preamp?) and rewire/replace the chicken head switch to select the pickups (neck, bridge, all, piezo for instance).
2. Pull the humbuckers out and use just the piezo for an EUB type sound. Would require replacement of the pickguard with something suitable.

Any thoughts on this would be appreciated. I will post some pictures of the fret wear and the pickguard soon (camera is in the car and I just got home from a gig).

Thank you in advance any suggestions. I'm in Los Angeles if you can recommend someone.