My Epi has a pair of gibson TB's, and I thank TBird1958 for this! It is as he said an almost drop in, the Gibson pups are just a bit wider so you have to route a bit, but it is really minimal work.
Also Gibsons are not as thick as epis, so you need to put something like a small block of wood under the pups to raise 'em (just adding extra foam doesn't work so good).
But boy they do sound good!