Do I need an adapter plate for gt500 tb on a c&l intake manifold? Also where is the best place to get the silicone coupler to attach to my intake tube (turbonetics turbo intake)?
^^ These guys are awesome. Used them for all my boost/vac lines. They'll have everything you need.
As for the GT500 TB, the C&L features an open oval inlet design instead of twin bores like the OEM and FRPP manifold. Part of the reason you need an adapter plate for the later 2 is because the larger throttle blades will actually make contact with the inlet bores, so the TB needs to be spaced forward. The other reason is the bolt holes on the GT500 TB don't match any NA type intake manifold inlet, as the TB was designed with the Eaton blower in mind. With the C&L you won't have those clearance issues with the manifold inlet. So if you're willing to do a little dremel work, all you should need to do is widen the bolt holes, or rather "move" the holes, so they line up with the manifold. Keep them tight of course, so the TB lines up on center. This is the route I would take, but I'm a cheap ass, if I don't have to spend $100-200 on an adapter plate, I won't lol.
No. And you need a 5" coupler to fit the bellmouth of the gt500 tb. Whats often done is a 5 inch to 3.5" coupler then a step down pipe from 3.5 back to 3". Since a 5" to 3" coupler is a bit of a unicorn.