My Baldwin went through a partial rebuilding in 2007 as you might recall. Because it was nearly 25 years old (much younger than your Gaveau), it needed less, but the job was still about $5,500 U.S., so not inexpensive. Luckily my tuner is also a technician and piano rebuilder with many years of experience, so the Baldwin was in good hands. What was done was this: Ronsen Wurzen hammers, shanks and flanges; Arledge Bass Strings; Mapes International Gold wires for the treble bridge; Chrome plated tuning pins one size larger; Crescendo wurzen conical key punchings on the front rail; Crescendo "accelerated" key punchings on the balance rail; replacement of about a dozen natural key coverings; and full regulation of the piano's action.
Here are some things I learned:
1) It is really best to move the piano out of the house to the rebuilder's shop. I started by having the work done in the home believing it would be OK, but little did I anticipate how noisy the restringing is when the new tuning pins have to be hammered into the pin block! My wife was quickly an unhappy camper, so I had to move the piano out ASAP. Otherwise, I might have been moved out.
2) If the existing pinblock will not be replaced, it's better to hand crank the old tuning pins out of the block rather than taking the easier route of reverse drilling them out with an electric drill attachment. Why, especially where it's less labor intensive just reverse-drilling them out? Because hand cranking them out produces less friction and heat than reverse drilling, and is thus less damaging to the pinblock. You'll appreciate the heat aspect when you hand crank the first pin out. If you drop it into the palm of you hand, it'll burn!
Reverse drilling makes them even hotter. To save expense, the rebuilder showed me how to do it properly, and I then cranked most of them out myself while he attended to other tasks.
3) Here is something you many not have anticipated: The rebuilder will tune the piano at least a couple of times just before you get the piano back. But it will NOT have tuning stability unfortunately. So be sure you have a good tuning lever on hand, as you'll be fixing a lot of notes yourself as you practice. He'll have to return to re-tune at fairly short intervals at first, which will gradually become longer as the piano regains full stability. This phenomenon could take more than a year. The strings have to fully stretch and conform around the hitchpins, bridge pins, and the tuning pins. The wires have to bend to micro-tolerances. If you want to accelerate the process somewhat, tune sharp to concert pitch rather than A440, thereby putting more tension on the strings. It's a bit more shrill in the room, but once stability is reached, you can drop it down to A440.
4) Make sure you get new felt strips under the strings directly in back of the tuning pins (some of the old strings might have worn completely through the felts, and especially the cloth under the copper-wound strings in the low bass such that they're actually contacting the metal plate. (This won't be apparent until the old strings are removed exposing the grooves--or holes--in the cloth.) Also be sure you get new damping ribbons in the waist-string area between the hitchpins and bridges in the tenor section of the scale. These aren't just for looks--they help control spurious and unpleasant vibrations. If the piano returns minus the ribbons, you'll notice it in the sound immediately!
I hope that helps.