I am an endorsing artist for Mike Lull's Thunderbird pickups, I have 2 Gibson 'Birds with Lull pickups plus a Lull 'Bird, so I've done what you're asking about twice.
To answer your questions....
Yes, Lull pickups will fit a modern (Post 1988) Gibson. In fact you should fill most of the pup routs with dense foam or wood or both as Lull pickups are much shallower than Gibson TB Plus. I'd suggest the metal bezels and the black spacer pieces to surround them as the new pups will be very close to the surface of the bass.
The pickups are the major part of your second question as there is not a tonal contribution that I can hear coming from the bridge, or woods assuming we're talking about good Mahogany. The neck construction uses threaded inserts and is far better and different than say a 7ender, it's much closer to sounding like a neck thru construction bass.
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Mike's pickups are reproductions of a specific Gibson '64 Thunderbird, it had 9K bridge and 8k neck pups and had "the sound", Mike's owned many Thunderbirds and knew what he wanted when having these made. Initially, Jason Lollar was approached to make them and he decided against doing it, his offering came along quite a bit later. Mike then went to TV Jones and later when Jones couldn't keep up with demand Seymour Duncan. As reproductions they're very accurate, even the covers are done by the same manufacturer Gibson used.
Thunderbucker Ranch offers excellent reproductions as well, their catalog includes several variations based on Gibson production throughout the '60s. Manufacturing process at the time was not so refined and as a result many pickups were overwound which created a tonally different pickup with a hotter more overdriven sound. Thunderbucker Ranch has recreated these variations which many of the guys here really like.
In looking for a suitable Gibson 'Bird I'd highly recommend finding an early re-issue from 1988 thru may '92 or so, the woodwork on them is reasonably nice and the bridge sits down on the bass much better. To my knowledge these years aren't considered highly collectable except for certain colors like Classic White so you should find one in your price with some patience.
Me and my '89 Thunderbird modified with Lull pickups, they're clear, warm and have just the right clank and growl for me.
) the only real difference is the finish, poly on the Epi and nitro on the Gibby but it's a class guitar by any standards
