Dude its one of the most popular cars on the planet, there is no shortage of parts for them.
What model have you got? Twincams have the 4age and rear disks. Bigger brakes can be had off other models (ae92, sv21)
Gearboxes are pretty much all interchangable (ie ae82, ae92, even 6 speeds from later models) You can get factory lsd boxes.
Search, and ye shall learn (twincam.org, twincam.org.au also)