I recently did some electrical work on my cousin's 1957 or 58 Gibson ES 125 like the one on this link
....only I noticed that the top is getting a bit of a valley down the center. The previous owner had cut a hole for a bridge pickup (also a P-90) and two holes for the corresponding v/t controls below the f hole. This valley is most pronounced at the bridge pickup and the bridge itself. No indication of a sag near the neck pu, or elsewhere really. My concern is that cutting that hole sacrificed the structural integrity of the top. We are not talking about a complete crushing here, instead, the top arches up like it is supposed to but as it starts to round off at the crest of the hill, it starts to dip down leaving about 3/32" - 1/8" gap between the solid stiff, but flexible plastic pickup ring and the guitar top and shows similar sag at the bridge. What is the best method of restoring the proper arch to the top of this guitar???? Should I install a sound post? Please advise. (He wants to keep that extra bridge PU by the way)
After installing new SD Antiquity pups for him, he noticed that the strings were buzzing a bit and it sounded dead acoustically. So I raised the action at the bridge and alleviated some tension in the TR, and now it's a bit high for him but the buzzing issue is better. We both agree that our intense scrutiny of the guitar afterward may be revealing buzzing and fretting out that was there to begin with, that we are only now catching. Though I did not have a chance to really sit down and play the guitar before working on the electronics as it was a quick job just before a show, so I'm going by his experience regarding this new found buzzing.
Could the top have shifted more since installing the new pickups causing the bridge to sag a little resulting in more buzz?
As a side note, just in case it was just a case of him not noticing it before, I picked up some other guitars of his and found his 63ish Epi Riviera was in serious need of TR adjustment as it had a critical backbow causing much string buzz, though the action was low like he likes it. He had not noticed a problem with this guitar. This makes me think the the Gib 125 is, as it was, before I worked on the pups. Just my thoughts on this issue, but please weigh in....